The relation between LBP and transitional vertebra was investigated in 312 subjects; 148 healthy individuals served as controls. An overall incidence of 0.65% lumbarization and 20.8% sacralization was found; of the latter, one third were partial and two-thirds complete. The incidence was markedly lower in women. No direct relation between sacralization, partial or complete, and LBP was found; this was based on interrelation of the LBP and control groups, with or without sacralization, to age, ethnic community, occupation, number of changes of occupation or place of employment, duration of LBP, and physical occupational requirements (sitting, standing, bending, sudden maximal effort). There is some evidence that LBP, when associated with sacralization, may be more severe.