The purpose of this retrospective study was to evaluate the clinical and radiological outcome of bilateral sacroiliac joint (SIJ) fusion, using a new technique, in patients with a chronic SIJ syndrome. Seventeen patients with chronic low back pain, with a positive response to specific diagnostic tests for the SIJ, were considered candidates for bilateral sacroiliac fusion. The surgical indication was based on the results of local anaesthetic joint infiltration, temporary external fixation or bone scan. Ten patients had had previous surgery on the lumbar spine. Bilateral posterior SIJ fusion was performed with internal fixation and decortication of the sacroiliac joint, using a separate approach to each joint. Local bone grafting was performed. At the time of follow-up (on average 39 months after surgery), 3 patients reported moderate or absent pain, 8 marked pain and 6 severe pain. Seven patients showed a symptomatic non-union; union occurred in only 6 cases. Eighteen percent of the patients were satisfied, but in the other 82% the results were not acceptable. Reoperation was performed in 65% of the patients. Our results with bilateral posterior SIJ fusion were disappointing, which may be related with difficulties in patient selection, as well as with surgical technique. Better diagnostic procedures and possibly other surgical techniques might provide more predictable results, but this remains to be demonstrated.