Localized pigmented villonodular synovitis (PVNS) of the knee is an uncommon entity, presenting with different clinical signs and symptoms. We report on a case of a 42-year-old woman who presented with a 3-year history of knee pain and mechanical problems such as locking. On examination she was found to have a palpable and painful mass over the anteromedial joint line. Magnetic resonance imaging (MRI) revealed a soft tissue mass in the anteromedial compartment of the knee joint. The lesion was completely resected arthroscopically, and histologic examination confirmed the diagnosis of localized PVNS. The patient was free of symptoms, and MRI examination showed no evidence of recurrence at 1-year follow-up.