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Sunlight is the principal environmental cause of melanoma and has also been implicated in the pathogenesis of melanocytic naevi. Epidemiological evidence indicates that childhood is a period during which melanocytes are susceptible to the effects of sunlight, yet little is known about the development of naevi in infancy. We conducted a survey of child-care centres to document the prevalence and anatomical distribution of melanocytic naevi among 193 young children aged 1-3 years in Brisbane, Australia (latitude 27°S). Naevi were counted on all skin surfaces except for the scalp, buttocks and genitalia. Overall, almost 90% of children in the study sample had at least 1 naevus of any size, and more than 30% of children had 10 or more naevi. Total naevus counts ranged from 0 to 45 and were strongly determined by age. When taken together, naevus densities were highest on exposed body sites such as the face and limbs; however the density of large naevi (> 5 mm) was significantly higher on the trunk than on the face, neck and ears. These data support the concept that melanocytic neoplasia commences early in life and that naevus evolution is influenced by the anatomical site of the target cell. Key words: naevus; melanoma; prevalence; risk factors; childhoodMelanocytic naevi remain the focus of scientific scrutiny because of their well-described epidemiological association with cutaneous melanoma. Whether naevi are precursors of melanoma or simply markers for inherent susceptibility to melanocytic proliferation remains an issue of debate; nevertheless it is clear that people with numerous melanocytic naevi are up to 10 to 20 times more likely to develop melanoma than people with very few naevi. 1,2 The premise underlying studies of naevi is that the factors that drive the development of naevi are likely to be implicated in the development of melanoma, since both types of lesions arise from melanocytes, the pigment-producing cells of the skin. While twin studies suggest that naevus number is a strongly heritable characteristic under genetic control, 3,4 there is considerable epidemiological evidence that an individual's naevus burden is strongly influenced by environmental factors. 5 Sunlight is the only environmental factor that has been credibly implicated in the development of both naevi and cutaneous melanoma 6,7 and it is widely inferred that melanocytes are particularly susceptible to the biological effects of sunlight during the "critical period" of early childhood. 8 Despite this, only a very few studies of naevi in the first years of life have ever been conducted. 6,9 Recently, interest has focused on differences in the occurrence of naevi in children across anatomical sites. 10 This is an important issue, since an understanding of site-specific naevus evolution in early life may help to explain the apparent differences in aetiology 11 and incidence of melanoma at different anatomical sites in adults. [12][13][14][15] Here we report the findings of a study of the prevalence and distribution of naevi in very you...