Arthroscopy is an indispensable tool in the diagnosis, treatment, and postoperative follow-up of pigmented villonodular synovitis (PVNS) and enables classification of PVNS into three forms: diffuse, localized, and mixed. A series of 13 cases of PVNS of the knee is presented; 12 patients underwent surgery. According to the anatomic type of PVNS found, the authors used extensive classic surgery or endoscopy. Follow-up averaged 4.2 years (range, 1-10 years). The best results were obtained in cases of localized PVNS. Overall, nine patients were totally asymptomatic at follow-up. Four patients experienced some pain when fatigued or with changes in the weather. There was no recurrence of symptoms.