Dear Editor,cne vulgaris is a chronic inflammatory disease affecting the pilosebaceous unit in the skin [1]. Isotretinoin is a synthetic vitamin A derivative using in severe cystic acne treatment. Pain and arthralgia are observed in 20% of patients treated with isotretinoin [2]; however sacroiliitis is rare and hip arthritis is even more rare. There was no article in the literature about a patient with sacroiliitis and hip arthritis together.A 30-year-old male patient who was suffering from severe pain on his left hip and leg for two days admitted to our clinic. His pain was very intense in the evening and the Visual analog scale (VAS) pain score was 8. He experienced morning stiffness for two days and about an hour on his left lower extremity. The patient had no history of inflammatory low back pain, skin lesion, bowel problem or infection. No pathology was found in rheumatologic examination. Family history was normal, however the patient was taking isotretinoin 20 mg/day for acne vulgaris about two months. The patient resorted to the brain surgery department before our clinic, the lumbar magnetic resonance imaging (MRI) was taken and no pathology was detected. The inspection of left leg and other body parts were normal but there was a pronounced skin dryness around the mouth periphery and face. There was mild sensitivity with palpation on left hip but the movements were limited and so painful. Flexion, abduction, and external rotation (FABER), flexion, adduction, and internal rotation (FADIR), sacroiliac compression, Mennel and Gaenslen tests were bilateral positive but more painful on left side. Lumbar range of motion was normal and there was no neurological deficit. Erythrocyte sedimentation rate (ESR) (33 mm/hr) and C-reactive protein (CRP) (3.84 mg/L) values were higher in the laboratory tests. Complete blood count, routine biochemical tests and HLA-B27 were negative. Bilateral bone narrow edema on iliac sides of sacroiliac joints and increased joint fluid on left hip was found on MRI (Figures 1a and 2a). As a result of all tests, the patient was diagnosed as bilateral sacroiliitis and left hip arthritis due to isotretinoin. The isotretinoin was ceased and nimesulide 2×100 mg, methylprednisolone 1×16 mg and lansoprazole 1×30 mg was started. A dramatic clinical response was obtained. A significant decrease was observed in the laboratory parameters on the seventh day (CRP: 0.06 mg/L, ESR: 5 mm/hr) and the VAS score was 3. Methylprednisolone was reduced and ceased. A repeat MRI performed five months later showed no evidence of left hip arthritis and sacroiliitis (Figures 1b and 2b) and the examination was completely normal.