A 42-year-old woman presented with a 3-week history of left knee pain and swelling. She had suffered dermatitis herpetiformis for 12 years, proved by skin biopsy. She had never been on gluten-free diet. Knee pain increased with motion and her gait was antalgic. On admission, she was mainly dependent on wheelchair due to pain and limitation. Treatment plan consisted of gluten-free diet, stretching and strengthening exercises, analgesic or nonsteroidal anti-inflammatory drugs when needed. She responded well to gluten-free diet. Association of joint involvement and dermatitis herpetiformis is more than just coincidental. Possible immunopathogenesis and role of gluten-free diet on arthritis treatment are discussed.