The magnetic resonance imaging characteristics of two surgically proven cases of pigmented villonodular synovitis are reported. On the short TR/TE pulse sequences, the synovium has an intermediate signal intensity. Long TR/TE pulse sequences show the synovium containing areas of increased signal interspersed with decreased signal. Hemosiderin deposition is believed to account for the areas of decreased signal; the increased signal results from fluid and inflamed synovium.