The associations of sun exposure, sunburn, skin color, and other constitutional characteristics with the density of nevi (2 mm or more in diameter) were assessed in a study of 410 secondary school children ages 14-15 years in Tasmania, Australia. Skin color was estimated by using a chromameter that measures across the visible light spectrum (400-700 nm). Skin color and lifetime history of sunburn were significant predictors of nevus density on the arms and legs of girls and boys and on the shoulders and backs of boys. The nevus density ratios between the highest and lowest exposure groups were 2.85 for the arms and legs of boys (P < 0.01), 2.19 for the arms and legs of girls (P < 0.01), and 1.72 (P = 0.03) for the shoulders and backs of boys. The increase in nevus density appeared to occur at lower levels of lifetime sunburn in children with light or medium skin than it did in children with darker skin. Darker-skinned children with a history of many sunburns ( > or = 11 lifetime sunburns) had a similar number of nevi compared with their lighter-skinned peers.