Malignant melanoma in children, adolescents, and young adults is unusual, especially before puberty. In children (age, 0-14 years), most primary lesions are thick and atypical (amelanotic, simulating pyogenic granuloma). In the population of adolescents and young adults (age, 15-39 years), melanoma is the third most common cancer, only behind lymphoma and breast cancer. Our study investigated the records of 89 patients diagnosed with cutaneous melanoma at age 0-39 years at Hospital das Clínicas, Medical School, University of São Paulo between 1992 and 2002. They were divided into group A (0-14 years of age) and group B (15-39 years of age). The histopathology of all cases was reexamined. Statistical analysis of the data presented was performed, and the obtained data were compared with the literature. The frequency of melanoma in the group aged 15-39 years was higher in women, and the most affected site was the trunk. Additionally, melanomas were more frequent at an earlier age in patients with family history of melanoma (P = 0.014). Most cases were diagnosed, at histopathology, as superficial spreading melanoma. Thick nodular melanomas with Breslow values higher than 2 mm were associated with lymph node metastasis (P < 0.05). Our study revealed that melanoma in children, adolescents, and young adults may present peculiar behavior and outcome, which might reflect the genetic and yet not fully unraveled pathogenesis of this complex disease.