Pigmented villonodular synovitis is an uncommon synovial disease which only rarely involves the hip. In a multicenter retrospective study, we identified 58 histologically-proven cases. There were 33 females and 25 males. Mean age at diagnosis was 38 years. In all but two cases, only one hip was involved; the right hip was affected somewhat more often (33 cases) than the left. Two patients probably had bilateral hip disease. Mean delay to diagnosis was four years. Pain was the presenting symptom in most cases. A palpable mass in the groin was found in six patients. Plain roentgenograms were considered normal in only three patients. Bony cysts were seen in 39 patients and kissing cysts in 19. Joint space narrowing was found in 40 patients and was diffuse in half the cases. Roentgenograms suggested pigmented villonodular synovitis in 63% of cases, osteoarthritis of the hip in 16%, and inflammatory hip disease in 14%. Additional imaging studies included opaque arthrography in 21 subjects, computed tomography in 23, magnetic resonance imaging in 11, and arthroscopy in 9. Initial treatment was osmic acid synoviorthesis in 14 patients, partial synovectomy in 9, and total synovectomy in 21; in addition, eight patients had insertion of a cup prosthesis and 13 had total arthroplasty of the hip. Treatment was successful in 65% of cases after a mean follow-up of three years; among the 35% of failures, there were seven recurrences (14%). Total hip arthroplasty was performed secondarily in nine patients. This study illustrates the diversity of roentgenological changes in pigmented villonodular synovitis of the hip and the high frequency of osteoarticular lesions precluding conservative treatment. Magnetic resonance imaging and/or arthroscopy should be used to establish the diagnosis at an early stage when conservative treatment with total synovectomy and synoviorthesis is most likely to be successful.