Pigmented villonodular synovitis (PVNS) is a rare proliferative synovial disorder of uncertain etiology. Two forms of this disorder, a localized (LPVNS) and diffuse (DPVNS) form, are well differentiated. The therapy of choice for LPVNS is arthroscopic partial synovectomy with excision of the lesion. Total synovectomy, whether done arthroscopically or through an open arthrotomy, is the recommended treatment for DPVNS. During an eight-year period 13 patients, six male and seven female, average age 28 years (range, 16 to 60 years) were treated for PVNS of the knee with arthroscopic synovectomy. Average follow-up was 84 months (range, 28 to 127 months). Four patients were affected by localized PVNS and were subjected to partial arthroscopic synovectomy (two to three portals) with a complete lesion excision. The remaining nine patients presented with the diffuse form of PVNS and all of them underwent total arthroscopic synovectomy (five portals). The diagnosis was confirmed by synovial biopsy. Each patient was evaluated before treatment and at final follow-up. Results were assessed clinically, radiographically and subjectively and were rated as excellent, good, fair, or poor. No complications or recurrences were noted in the LPVNS group, and all four patients were rated as excellent. In the DPVNS group, eight patients were rated as excellent and one patient was rated as fair and it was the patient who suffered the only recurrence in our case series. No relevant complications were encountered. No cases of infection, joint stiffness or neurovascular lesions were seen. Arthroscopy has become the golden standard in treatment of LPVNS, and can undoubtedly give results that are as good as with open synovectomy when treating DPVNS, if performed by an experienced arthroscopic surgeon.