Pigmented villonodular synovitis (PVNS) has a high but variable recurrence rate. Prior studies do not compare recurrence-free survival (RFS) for various surgical approaches or salvage surgery for relapse. We therefore determined: (1) RFS after excision; (2) RFS after salvage surgery for relapse; (3) factors associated with relapse. We retrospectively reviewed the medical records of 49 patients with previously untreated PVNS of the knee (12 localized, 37 diffuse) who were treated with synovectomy from 1991 to 2008; there were 22 males and 27 females, with mean age of 35.2 years (range, 10-73). Minimum followup was 1 year (mean, 6.2 years; range, 1-13). Twenty-one patients had a relapse. The RFS for index surgery was 75% and 53%; and for salvage surgery was 71% and 52% at 2 and 5 years respectively. The RFS was 95% for open versus 62% for arthroscopic synovectomy at 2 years, 71% and 41% at 5 years. The RFS was 91% for localized and 70% for diffuse PVNS at 2 years, 73% and 48% at 5 years. Diffuse disease (RR = 4.49) and arthroscopic synovectomy (RR = 3.30) were associated with relapse. Recurrence was frequent after synovectomy. Reexcision can salvage relapses as successfully as excision for primary disease; however, morbidity was associated with additional surgeries. Level of Evidence: Level IV, therapeutic study. See Guidelines for Authors for a complete description of levels of evidence.