Most melanocytic nevi develop in childhood, and several factors have been consistently shown to be related to higher numbers of nevi: lighter skin, lighter hair color, blue or green eyes, and higher levels of sun exposure. Because the risk factors for nevi closely match the risk factors for melanoma, understanding nevus development may improve our understanding of the pathophysiology of melanoma. In this longitudinal observational study, Crane et al described the development of nevi in children aged 3 to 8 years in a birth cohort in Colorado. Nevus development patterns were similar to those reported in the United Kingdom but were notably different from those in children in other Northern European countries and Australia, particularly with respect to the small size of the nevi and the patterns of nevus development on intermittently and chronically exposed body sites. These differences highlight the importance of studying nevus development in various regions of the world.