Osteoid osteoma of the acetabulum can be expected to cause nonspecific symptoms of hip inflammation. In a sixteen year old girl, investigation by routine radiographs and a bone scan suggested a focus of inflammation with a nidus and sclerosis of the acetabulum and overgrowth of the head and neck of the femur. Removal of the lesion by an anterior approach with dislocation of the hip gave excellent results when seen after three years with a normal gait and normal hip motion.