The horizontal and vertical diameters of the pedicles of the lumbar vertebrae were measured from plain anteroposterior radiographs of the lumbar spines of male and female subjects aged from 10 to 65 y. The results showed that there were significant differences between the pedicle diameters of males and females. Horizontal diameters ranged from 7.4 to 13.6 mm in females and from 7.5 to 14.2 mm in males. Female vertical diameters ranged from 14.2 to 18.2 mm whilst male vertical diameters ranged from 14.8 to 20.7 mm. Generally, there was a cephalocaudal increase of diameters in both sexes. Significant age-related variations of pedicle diameters were noted at all segmental levels. Within the adolescent group (10-19.9 y), the diameters of the 10-14.9 y group and 15-19.9 y group differed significantly (P < 0.001). When the pedicle diameters of the individual age groups were compared, the pedicles of the 10-19.9, 20-29.9, 30-34.9, 40-49.9, and 50+ y groups were found to be significantly different from each other. The evidence suggests that pedicle diameters undergo continuous change throughout the age range studied. The changes are characterised by increase of diameters in some age groups and decrease in others, but there was an overall increase of both vertical and horizontal diameters as the age groups were followed from the youngest to the oldest. The pattern of variation with age differed for horizontal and vertical diameters. After the 5th decade, female horizontal and vertical diameters showed a tendency to increase while male diameters decreased.