We describe a case of localized gastrocnemius myositis which developed with flare-up of Crohn's disease. A 21-year old male patient with an 8-year history of Crohn's disease presented with pain and tenderness in both calves without recent abdominal symptoms. Electromyography and gastrocnemius muscle biopsy revealed evidence of inflammatory myositis. Magnetic resonance imaging (MRI) showed bilateral symmetrical diffuse increased signal intensity in T2 weighted images in both gastrocnemius muscles and patchy contrast enhancement. Subsequent gastrointestinal investigation revealed active inflammation of colon with multiple pseudopolyps and enteroenteric fistula on which we com-menced oral prednisolone of 30 mg daily. His pain on both calves was improved and muscle enzymes became normal. Following dose reduction of prednisolone, azathioprine 50 mg daily was started considering the patient's active Crohn's disease on endoscopic findings prior to the development of overt abdominal symptoms. This is the first case report of localized gastrocnemius myositis associated with Crohn's disease described in Korea. Calf myositis re-sponded to corticosteroid well and did not recur with maintenance therapy using azathioprine and mesalazine.