INTRODUCTION: The acronym SAPHO was introduced in 1987 to unify the various descriptions of a seronegative arthritis associated with skin manifestations and to show synovitis, acne, pustulosis, hyperostosis, and osteitis with and without sterile multifocal osteomyelitis. The etiology of SAPHO syndrome is unknown, but an association with infection by semipathogenic bacteria like Propionibacterium acnes has been suggested. We conducted an interventional study of SAPHO patients receiving antibiotics. METHODS: Thirty-seven patients met the clinical criteria of SAPHO syndrome, 21 of them underwent a needle biopsy of the osteitis lesion, and 14 of them showed positive bacteriological cultures for P. acnes. Thirty patients (14 bacteriological positive and 16 without biopsy) were treated with antibiotics for 16 weeks. The activity of skin disease and osteitis were assessed by a physician using a scoring model (from 0 to 6). In addition, patients completed a Health Assessment Score (HAS, from 0 to 6). The erythrocyte sedimentation rate was determined and a MRI (of the osteitis lesion, radiologic activity score from 0 to 2) was performed in week 1 (W1), week 16 (W16), and week 28 (W28, 12 weeks after antibiotics). RESULTS: Twenty-seven patients continued the medication (azithromycin, n = 25, 500 mg twice a week; clindamycin, n = 1, 300 mg daily; or doxycycline, n = 1, 100 mg daily) for 16 weeks. After W16 the scores for MRI (1.5 to 1.1, P = 0.01), skin activity (3.2 to 1.2, P = 0.01), osteitis activity (4.0 to 2.1, P = 0.02), and HAS (3.3 to 2.1, P = 0.01) decreased significantly. However, this was followed by increasing values for MRI scores (1.2 to 1.4, P = 0.08), skin activity (1.2 to 1.7, P = 0.11), osteitis activity (1.9 to 2.7, P = 0.01), and HAS (2.2 to 3.3, P = 0.02) from W16 to W28. The comparison of the scores in W1 and W28 in these 12 patients showed no significant differences. CONCLUSIONS: For the period of application, the antibiotic therapy seems to have controlled the disease. After antibiotic discontinuation, however, disease relapse was observed. SAPHO syndrome thus groups with other chronic inflammatory arthropathies with a need for permanent therapy.