Lumbosacral transitional vertebrae (LSTV) are common congenital anomalies of the human spine. In LSTV, either the fifth lumbar vertebra may show assimilation to the sacrum (sacralisation), or the first sacral vertebra may show transition to a lumbar configuration (lumbarisation). Although the condition has an incidence of over 12% in the general population, knowledge about the exact clinical implications is still lacking. The association between LSTV and low back pain has been debated since it was first described by Bertolotti almost a century ago. Furthermore, several conflicting studies have been published regarding the association of LSTV with other spinal pathology. There seems to be a relation with early disc degeneration above the LSTV in young patients. However, these differences fade with age as they are masked by other degenerative changes of the spine. From a practical view-point, failure to recognise and to number LSTV during spinal surgery may have serious consequences.