Hibernate version:
2.1

Are the Collection wrappers used by Hibernate multi-thread safe? If I have a Map loaded by Hibernate (e.g. an object has a map of properties). Is the Map thread safe for multiple simultaneous put() operations across different threads?

In most of my code I had used the various Collections.sychronizedXYZ() methods (and now the 1.5 concurrent collections). But with Hibernate, the Map/List is a wrapper set by Hibernate when the object is loaded. Presumably I don't want to lose the collection wrapper Hibernate has supplied?

No, they're not. Synchronize any blocks that refer to collections that might be used in multiple threads.