This report describes the case of a patient with a 14-month course of severe oligoarthritis associated with acne. Pure cultures of Propionibacterium acnes were isolated from synovial tissue and synovial fluid specimens collected from the same joint after a 4-month interval. After 2 months of treatment with roxithromy-cin 300 mglday, rifampicin 1,200 mglday, and a nonste-roidal antiinflammatory drug (NSAID), followed by 4 months of treatment with azithromycin 1 gm/week and an NSAID, the synovitis persisted. Cultures of skin lesions and synovial fluid at this time were negative. Although P acnes has previously been isolated from bone specimens obtained from patients with osteitis associated with acne, this is the first report of the isolation of this microorganism from the synovial tissue of a patient with arthritis associated with acne. Our findings raise the question of the role of P acnes in the pathogenesis of arthritis associated with acne. Acne is a chronic inflammatory disease of the pilosebaceous follicles, characterized by the formation of comedones and erythematous papules and pustules, and less frequently, by nodules or cysts and ulcerative lesions that can lead to definitive scarring. Acne can be differentiated into acne vulgaris (thc common form that begins classically in thc prepubertal period and resolves by the mid-20s; significant lesions can still bc sccn in 3%