A low-overhead conditional synchronization instruction operates on a synchronization variable which includes a lock bit, a state specification, and bits for user-defined data. The instruction specifies the memory address of the synchronization variable and a condition. During the synchronization instruction the condition is compared to the state specification within an atomic region. The match succeeds if the condition matches the state specification and the lock bit is clear. The synchronization instruction may operate with a cache under a cache coherency protocol, or without a cache, and may include a timeout operand.