Objective To explore the technique of arthroscopic treatment of local ized pigmented villonodular synovitis of the knee and to evaluate its cl inical results. Methods From February to December 2006, 22 cases of local ized pigmented villonodular synovitis of the knee were treated by arthroscopic excision of the focus and partial synovectomy. There were 8 males and 14 females, with an average age of 24 years old (16 to 35 years old). Eight patients had a trauma history, the others had no obvious inducement. The disease course was from 1 month to 30 months with an average of 10 months. The Lysholm score was 68.5 ± 8.2, and the International Knee Documentation Committee (IKDC) score was 72.7 ± 5.2 before operation. MRI showed that 20 knees had definite focuses and 2 had no ones. In all the cases, routine arthroscopic approach combined with assistant approach adjacent to the focus was used. Results All the patients were diagnosed as having local ized pigmented villonodular synovitis of the knee by pathological examination. The incisions healed at stage I. No compl ications occurred after operation. All patients were followed up 18-28 months (average 22 months). The angle of genuflex was less than 90° in 2 cases after 6 weeks, and the range of motion of the knee was recovery after manipulation release. At last followup, MRI showed no recurrence was found in 19 patients. The IKDC score was 92.8 ± 2.4, and the Lysholm score was 94.5 ± 3.5, respectively, indicating significant differences when compered with before operation (P lt; 0.01). Conclusion Local ized pigmented villonodular synovitis of the knee can be effectively treated by arthroscopic excision of the focus along with a rim of surrounding healthy synovium with most minimal invasive and best knee function.