Presence of large numbers of acquired melanocytic nevi is a strong risk factor for malignant melanoma in adults. A series of studies conducted over the past 10 to 15 years have shown that the lighter skin color, propensity to burn rather than to tan in the sun, and frequent episodes of childhood sunburn increase nevus prevalence in childhood and adolescence. Solar ultraviolet radiation exposure itself has been implicated in both the genesis of new nevi in children and the disappearance of nevi in older adult life.