Propionibacterium acnes is an anaerobic bacillus implicated in certain chronic arthritides. This report describes an HLA-B27+ 17-year-old woman with acne vulgaris who presented with rapidly destructive arthritis in the left shoulder as well as an evolving left subclavicular adenopathy. One year later, arthritis was detected in the left knee; the inflammatory synovial fluid was sterile. Growth of P acnes was observed in cultures of the shoulder synovium and lymph nodes, but polymerase chain reaction was negative for Borrelia, Chlamydia, and Ureaplasma DNA. Three months of treatment with amoxicillin and rifampicin led to clinical disappearance of the oligoarthritis, but arthritis recurred in the left knee after discontinuation of therapy. On biopsy, bacteria were undetectable in the knee synovium, but chronic arthritis was evident histologically. Antibiotics were reintroduced for 12 months and were again effective against the clinical symptoms. Although the asymmetry, histologic features, arthritis-acne association, and genetic predisposition of this chronic destructive oligoarthritis would seem to indicate a reactive arthropathy, the isolation of P acnes from 2 distinct specimens prompted us to propose calling this a case of septic-reactive arthritis, which is further supported by the absence of progression after antibiotic therapy and the persistence of the rheumatism. To our knowledge, this is the first demonstration of the efficacy of prolonged antibiotic therapy on the joint manifestations of chronic rheumatism associated with acne.