Knee locking is a highly incapacitating condition attributable to mechanical or functional factors. Pain, mostly of capsuloligamentous or intraosseous origin, is the cause of functional locking. Meniscal injuries are the most frequent arthroscopic finding in the locked knee, due to mechanical factors. We describe a patient experiencing locking during extension whose history and examination suggested a tear of the anterior horn of the lateral meniscus of the right knee; a diagnostic/therapeutic arthroscopy revealed an intraarticular gouty tophus growing from the anterior horn of the lateral meniscus.