The obturator externus bursa has been described as a potential bursa between the tendon of the obturator externus muscle and the posterior hip capsule. Although pathologic involvement of the iliopsoas bursa by intraarticualr hip disease has been extensively described, obturator externus bursa has not been fully investigated. We describe a patient who presented with hip pain and limited range of motion. Her magnetic resonance imaging of pelvis revealed an enhancing cystic lesion that extends inferomedially displacing obturator externus muscle and mild synovitis of the right hip. She was diagnosed as having obturator externus bursitis, and after symptomatic treatment pain and limited range of motion disappeared. The obturator externus bursa is a potential communication of the hip joint, can be a site of disease spread from the hip joint, and can be identified with magnetic resonance imaging. (J Korean Acad Rehab Med 2007; 31: 490-492)