diff --git a/src/main/java/com/google/gwtorm/client/OrmDuplicateKeyException.java b/src/main/java/com/google/gwtorm/client/OrmDuplicateKeyException.java
new file mode 100644
index 0000000..0874895
--- /dev/null
+++ b/src/main/java/com/google/gwtorm/client/OrmDuplicateKeyException.java
@@ -0,0 +1,26 @@
+// Copyright 2009 Google Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package com.google.gwtorm.client;
+
+/** Indicates one or more entities were concurrently inserted with the same key. */
+public class OrmDuplicateKeyException extends OrmException {
+  public OrmDuplicateKeyException(final String msg) {
+    super(msg);
+  }
+
+  public OrmDuplicateKeyException(final String msg, final Throwable why) {
+    super(msg, why);
+  }
+}
diff --git a/src/main/java/com/google/gwtorm/jdbc/JdbcAccess.java b/src/main/java/com/google/gwtorm/jdbc/JdbcAccess.java
index bd08a98..aa5775f 100644
--- a/src/main/java/com/google/gwtorm/jdbc/JdbcAccess.java
+++ b/src/main/java/com/google/gwtorm/jdbc/JdbcAccess.java
@@ -81,8 +81,7 @@
     try {
       return schema.getConnection().prepareStatement(sql);
     } catch (SQLException e) {
-      linkCause(e);
-      throw new OrmException("Prepare failure\n" + sql, e);
+      throw convertError("prepare SQL\n" + sql + "\n", e);
     }
   }
 
@@ -123,8 +122,7 @@
         ps.close();
       }
     } catch (SQLException e) {
-      linkCause(e);
-      throw new OrmException("Fetch failure: " + getRelationName(), e);
+      throw convertError("fetch", e);
     }
   }
 
@@ -148,8 +146,7 @@
         ps.close();
       }
     } catch (SQLException e) {
-      linkCause(e);
-      throw new OrmException("Fetch failure: " + getRelationName(), e);
+      throw convertError("fetch", e);
     }
   }
 
@@ -172,8 +169,7 @@
         ps.close();
       }
     } catch (SQLException e) {
-      linkCause(e);
-      throw new OrmException("Insert failure: " + getRelationName(), e);
+      throw convertError("insert", e);
     }
   }
 
@@ -196,8 +192,7 @@
         ps.close();
       }
     } catch (SQLException e) {
-      linkCause(e);
-      throw new OrmException("Update failure: " + getRelationName(), e);
+      throw convertError("update", e);
     }
   }
 
@@ -220,8 +215,7 @@
         ps.close();
       }
     } catch (SQLException e) {
-      linkCause(e);
-      throw new OrmException("Delete failure: " + getRelationName(), e);
+      throw convertError("delete", e);
     }
   }
 
@@ -242,10 +236,11 @@
     }
   }
 
-  private static void linkCause(final SQLException e) {
-    if (e.getCause() == null && e.getNextException() != null) {
-      e.initCause(e.getNextException());
+  private OrmException convertError(final String op, final SQLException err) {
+    if (err.getCause() == null && err.getNextException() != null) {
+      err.initCause(err.getNextException());
     }
+    return schema.getDialect().convertError(op, getRelationName(), err);
   }
 
   protected abstract T newEntityInstance();
diff --git a/src/main/java/com/google/gwtorm/jdbc/JdbcSchema.java b/src/main/java/com/google/gwtorm/jdbc/JdbcSchema.java
index 4327560..17b6cc0 100644
--- a/src/main/java/com/google/gwtorm/jdbc/JdbcSchema.java
+++ b/src/main/java/com/google/gwtorm/jdbc/JdbcSchema.java
@@ -41,6 +41,10 @@
     return conn;
   }
 
+  public final SqlDialect getDialect() {
+    return dbDef.getDialect();
+  }
+
   public void createSchema() throws OrmException {
     final SqlDialect dialect = dbDef.getDialect();
     final SchemaModel model = dbDef.getSchemaModel();
@@ -84,7 +88,7 @@
         st.close();
       }
     } catch (SQLException e) {
-      throw new OrmException("Sequence query failed", e);
+      throw convertError("sequence", query, e);
     }
   }
 
@@ -102,4 +106,12 @@
       conn = null;
     }
   }
+
+  private OrmException convertError(final String op, final String what,
+      final SQLException err) {
+    if (err.getCause() == null && err.getNextException() != null) {
+      err.initCause(err.getNextException());
+    }
+    return getDialect().convertError(op, what, err);
+  }
 }
diff --git a/src/main/java/com/google/gwtorm/schema/sql/DialectH2.java b/src/main/java/com/google/gwtorm/schema/sql/DialectH2.java
index adf6be2..3793d86 100644
--- a/src/main/java/com/google/gwtorm/schema/sql/DialectH2.java
+++ b/src/main/java/com/google/gwtorm/schema/sql/DialectH2.java
@@ -1,8 +1,26 @@
 package com.google.gwtorm.schema.sql;
 
+import com.google.gwtorm.client.OrmDuplicateKeyException;
+import com.google.gwtorm.client.OrmException;
+
+import java.sql.SQLException;
+
 /** Dialect for <a href="http://www.h2database.com/">H2</a> */
 public class DialectH2 extends SqlDialect {
   @Override
+  public OrmException convertError(final String op, final String entity,
+      final SQLException err) {
+    switch (getSQLStateInt(err)) {
+      case 23001: // UNIQUE CONSTRAINT VIOLATION
+        return new OrmDuplicateKeyException(entity, err);
+
+      case 23000: // CHECK CONSTRAINT VIOLATION
+      default:
+        return super.convertError(op, entity, err);
+    }
+  }
+
+  @Override
   public String getNextSequenceValueSql(final String seqname) {
     return "SELECT NEXT VALUE FOR " + seqname;
   }
diff --git a/src/main/java/com/google/gwtorm/schema/sql/DialectPostgreSQL.java b/src/main/java/com/google/gwtorm/schema/sql/DialectPostgreSQL.java
index 5d2391c..83fe3fc 100644
--- a/src/main/java/com/google/gwtorm/schema/sql/DialectPostgreSQL.java
+++ b/src/main/java/com/google/gwtorm/schema/sql/DialectPostgreSQL.java
@@ -1,5 +1,9 @@
 package com.google.gwtorm.schema.sql;
 
+import com.google.gwtorm.client.OrmDuplicateKeyException;
+import com.google.gwtorm.client.OrmException;
+
+import java.sql.SQLException;
 import java.sql.Types;
 
 /** Dialect for <a href="http://www.postgresql.org/>PostgreSQL</a> */
@@ -10,6 +14,22 @@
   }
 
   @Override
+  public OrmException convertError(final String op, final String entity,
+      final SQLException err) {
+    switch (getSQLStateInt(err)) {
+      case 23505: // UNIQUE CONSTRAINT VIOLATION
+        return new OrmDuplicateKeyException(entity, err);
+
+      case 23514: // CHECK CONSTRAINT VIOLATION
+      case 23503: // FOREIGN KEY CONSTRAINT VIOLATION
+      case 23502: // NOT NULL CONSTRAINT VIOLATION
+      case 23001: // RESTRICT VIOLATION
+      default:
+        return super.convertError(op, entity, err);
+    }
+  }
+
+  @Override
   public String getNextSequenceValueSql(final String seqname) {
     return "SELECT nextval('" + seqname + "')";
   }
diff --git a/src/main/java/com/google/gwtorm/schema/sql/SqlDialect.java b/src/main/java/com/google/gwtorm/schema/sql/SqlDialect.java
index 82aa4b2..2565513 100644
--- a/src/main/java/com/google/gwtorm/schema/sql/SqlDialect.java
+++ b/src/main/java/com/google/gwtorm/schema/sql/SqlDialect.java
@@ -14,10 +14,12 @@
 
 package com.google.gwtorm.schema.sql;
 
+import com.google.gwtorm.client.OrmException;
 import com.google.gwtorm.client.Sequence;
 import com.google.gwtorm.schema.ColumnModel;
 import com.google.gwtorm.schema.SequenceModel;
 
+import java.sql.SQLException;
 import java.sql.Types;
 import java.util.HashMap;
 import java.util.Map;
@@ -69,6 +71,41 @@
     return true;
   }
 
+  protected static String getSQLState(SQLException err) {
+    String ec;
+    SQLException next = err;
+    do {
+      ec = next.getSQLState();
+      next = next.getNextException();
+    } while (ec == null && next != null);
+    return ec;
+  }
+
+  protected static int getSQLStateInt(SQLException err) {
+    final String s = getSQLState(err);
+    if (s != null) {
+      try {
+        return Integer.parseInt(s);
+      } catch (NumberFormatException e) {
+        return -1;
+      }
+    }
+    return 0;
+  }
+
+  /**
+   * Convert a driver specific exception into an {@link OrmException}.
+   * 
+   * @param op short description of the operation, e.g. "update" or "fetch".
+   * @param entity name of the entity being accessed by the operation.
+   * @param err the driver specific exception.
+   * @return an OrmException the caller can throw.
+   */
+  public OrmException convertError(final String op, final String entity,
+      final SQLException err) {
+    return new OrmException(op + " failure on " + entity, err);
+  }
+
   public String getCreateSequenceSql(final SequenceModel seq) {
     final Sequence s = seq.getSequence();
     final StringBuilder r = new StringBuilder();