The causes of cutaneous melanoma among children under 15 years are largely unknown. We report the findings of an epidemiological study of childhood melanoma in Queensland, Australia, which has the highest incidence rates in the world. All 61 cases of melanoma in children less than 15 years notified to the Queensland Cancer Registry 1987-1994 were eligible to participate in a population-based, case-control study. Data were collected through structured, face-to-face interviews with parents and skin examinations of the 52 participating cases and 156 age- and sex-matched controls. The strongest determinants of melanoma risk found among Queensland children were constitutional factors, including the presence of more than 10 naevi greater than 5 mm in diameter (RR 9.9, 95% CI 2.5-38.9), heavy facial freckling (RR 6.4, 95% CI 1.9-21.6), an inability to tan on exposure to the sun (RR 8.8, 95% CI 2.1-36.2) and a family history of melanoma (RR 4.2, 95% CI 1.9-9.3). These factors remained significantly associated with melanoma after adjusting for other risk factors. No measures of acute or chronic exposure to solar UV radiation were associated with childhood melanoma in our study. Established risk factors, including giant congenital naevi and xeroderma pigmentosum, were not present among any of the children in the study. Melanoma in childhood appears to have similar epidemiologic characteristics to the adult form of the disease, being associated with a cluster of phenotypic attributes indicating cutaneous sensitivity to the effects of sun exposure. Our findings support the contention that childhood melanoma occurs in susceptible individuals with a low threshold for pigment cell tumorigenesis. From a public-health perspective, children at elevated risk for melanoma can be identified on the basis of phenotype and family history.