Sun exposure is the main environmental risk factor for the development of melanocytic nevi. Although the general association is not disputed, the interplay between intense intermittent and the cumulative amount of sun exposure in defining the promoting effect on melanocytic nevus development is an area of debate. Trained staff members ascertained total body counts of melanocytic nevi in a cross-sectional study of 2,189 children 6-7 years of age who were recruited in two German centers in 2002. Their parents provided information about a variety of exposure factors. The distribution of melanocytic nevi was skewed markedly to the right; therefore, a negative binomial regression model provided the appropriate framework for a multivariable analysis. A steep gradient with respect to the (adjusted) number of melanocytic nevi was apparent only for the frequency of vacation episodes associated with sun exposure in areas with an intense ultraviolet radiation. In contrast, no such gradients were found for the cumulative duration of vacation sun exposure in such areas or for any variable related to vacation sun exposure in areas with a low ultraviolet radiation. This observation supports the hypothesis that intermittent exposure to high doses of ultraviolet radiation plays an especially important role in nevus development.