Sun exposure in both childhood and adult life represents the main environmental risk determinant for cutaneous melanoma. However, little is known about the joint effects of sun exposure during early and later life on melanoma risk. A case-control study in Belgium, Germany and France conducted in 1991-1992 suggests that the melanoma risks attached to indicators related to sun exposure appear to combine their effects in an additive way. We therefore constructed composite indices of sun exposure during childhood and during adulthood, assuming additive combinations of melanoma risk associated with each indicator of sun exposure. Logistic regression modeling showed that the melanoma risk associated with a given level of sun exposure during adulthood increased with higher sun exposure during childhood, but the increase in risk was higher than the simple addition of melanoma risk associated with sun exposure during childhood or adulthood. In turn, high sun exposure during childhood constituted a significant risk factor for melanoma only if there was substantial sun exposure during adult life. We thus suggest that sun exposure during childhood and during adulthood would be interdependent as far as their impact on melanoma risk is concerned. Our results support the hypothesis by which the important contribution of sun exposure during childhood in melanoma occurrence is not properly assessed by retrospective epidemiologic studies. Sun avoidance during childhood would have a greater impact on melanoma risk than sun avoidance during adulthood.