We surgically treated 16 patients with Bertolotti's syndrome (chronic, persistent low back pain and radiographically diagnosed transitional lumbar vertebra). Eight had posterolateral fusion and another eight resection of the transitional articulation. Thirteen patients had in addition to the chronic low back pain, suffered from repeated episodes or chronic sciatica. In six cases with resection treatment, local injections were administered at the transitional articulation before deciding for resection of the transitional joint; each patient reported transient relief of pain, while this preoperative test did not correlate with successful outcome of treatment. Six patients had to be treated with second operations. Ten of the 16 operatively treated patients showed improvement of the low back pain, and this result was similar in the group treated with fusion and in that treated with resection. Seven had no low back pain at follow-up, and the improvement according to the Oswestry pain scale was similar in the two groups, and statistically significant. Eleven patients still had persisting episodes of sciatica (versus 13 preoperatively). The average disability according to the Oswestry total disability scale was 30%, corresponding with moderate outcome, and both operatively treated groups did equally well. At follow-up the first disc above the fused segments was found to be degenerated in seven out of eight cases, and in the group treated with resection the first disc above the transitional vertebra was degenerated in five cases.(ABSTRACT TRUNCATED AT 250 WORDS)