Sex differences in the Dutch standardisation sample of the WISC-R are analysed. The results correspond very closely to the sex differences in the Scottish and American standardisation samples. Boys scored significantly higher on the general intelligence factor and on the verbal and visuospatial factors. Girls scored higher on the perceptual speed/memory factor. There was no effect of age on sex differences. One of the causes for the higher scores for boys on the general and verbal factors is the relatively substantial sex difference on the Information subtest.