Bertolotti's syndrome is characterised by anomalous enlargement of the 
transverse process(es) of the most caudal lumbar vertebra which may articulate 
or fuse with the sacrum or ilium and cause isolated L4/5 disc disease. We 
analysed the elective MR scans of the lumbosacral spine of 769 consecutive 
patients with low back pain taken between July 2003 and November 2004. Of these 
568 showed disc degeneration. Bertolotti's syndrome was present in 35 patients 
with a mean age of 32.7 years (15 to 60). This was a younger age than that of 
patients with multiple disc degeneration, single-level disease and isolated disc 
degeneration at the L4/5 level (p </= 0.05). The overall incidence of 
Bertolotti's syndrome in our study was 4.6% (35 of 769). It was present in 11.4% 
(20 patients) of the under-30 age group. Our findings suggest that Bertolotti's 
syndrome must form part of a list of differential diagnoses in the investigation 
of low back pain in young people.