Osteoid osteoma in the acetabulum is very rare and the surgical extirpation is difficult. We present a case of osteoid osteoma in the posteroinferior portion of the acetabulum which was treated with arthroscopic excision. A 29-year-old woman presented with 18 months of pain in the left groin. Computed tomography suggested an osteoid osteoma in the posteroinferior portion of the acetabulum. Arthroscopic excision of the lesion was performed with the aid of image intensifier. The patient's symptoms disappeared immediately after the surgery. This case report shows that arthroscopic excision is possible in a lesion in the posteroinferior portion in the acetabulum, which previously deemed inaccessible arthroscopically.