The aim of this study was to assess longitudinally the development of melanocytic naevi in children around the time of their puberty. In Queensland, Australia, 102 schoolchildren born mostly in 1977 or 1978, were examined annually on four occasions from 1990. All naevi on the body except for the scalp and parts covered by a bathing suit were counted by an experienced research nurse or trained assistant according to a set protocol. In addition, each subject's pigmentary characteristics were recorded and height, weight and pubertal status were assessed annually. The findings confirmed that the average number of naevi and average density of naevi (count per m2) on the whole body in boys and girls increase significantly with increasing age and increases were also seen on each of the following anatomic sites: face and neck, back and shoulders, and upper and lower limbs. Children who had a high baseline naevus count, or a large increase in skin surface area during the 3-year follow-up period had the highest absolute increases in naevus count but the smallest proportionate increases. Associations between baseline naevus counts and male sex, light brown or blonde hair, blue or hazel eyes, facial freckling and a tendency to sunburn, which have been previously reported, were also found. However, the independent relations of each of these factors to the increase in new naevi were more complex, once the effects of high naevus counts at baseline and increases in skin surface area were taken into account. No association was found between the incidence of naevi and height, body mass index or time of onset of puberty in this group of adolescent subjects. Beyond personal characteristics, period of birth may also influence the development of naevi, since there has been an apparent increase in naevi in the Australian children in this and other recent studies compared with naevus counts among Australian children of previous generations of comparable age living in similar environments.