We describe the medical management of an acetabular osteoid osteoma in an 11-year-old girl. There was a 2-year delay until proper diagnosis of the patient’s pathology was made. Accurate localization of the nidus in the subchondral bone, involving the cartilage, is difficult on the basis of plain radiographs. All imaging methods, including computed tomography, MRI, and bone scintigraphy, were used to confirm the diagnosis. We proposed medical treatment to avoid possible severe complications from surgical intervention. At the patient’s latest follow-up visit, after 2 years of medical treatment with NSAIDs, there is complete healing of the osteoid osteoma and there is no sign of recurrence.