We present the case of a 16-year-old boy with an 18-month history of pain in the left groin for 18 months. In addition to the simple radiographic examination, magnetic resonance imaging, bone scan, and computed tomography were necessary to finally diagnose an acetabulum osteoid osteoma (AOO). Excision of the lesion was performed arthroscopically and pathologic testing confirmed the diagnosis. The patient's symptoms disappeared immediately after the surgery, and had not reappeared as of the 6-month postoperative evaluation. We conclude that arthroscopic excision of an AOO is possible and avoids the aggressive open approach as well as operative hip dislocation.