CT scan of the pelvis of a 33-year-old lady with low back pain. X-rays were normal as was an MRI of the lumbar spine. A bone scan showed increased activity in the ilium adjacent to the sacroiliac joint, and a CT showed a dense sclerotic lesion. This would have been typical for fibrous dysplasia radiologically, but this did not explain the pain. CT-guided needle biopsy confirmed the diagnosis. This CT image clearly shows the lesion and the path of the biopsy.