Abstract: A multithreaded processor and a method for performance monitoring within a multithreaded processor are described. According to the present invention, execution circuitry within the multithreaded processor executes instructions in an active thread among first and second concurrent threads, while buffering circuitry buffers instructions and/or data of an inactive one of the first and second concurrent threads. Thread switch logic in the multithreaded processor switches threads by activating the inactive thread and inactivating the active thread. The operation of the multithreaded processor is monitored by a performance monitor, which records occurrences of an event generated by switching threads.