Melanoma may arise from a very giant congenital melanocytic nevus even in the first several years of life. Therefore, excision of a giant congenital melanocytic nevus should be considered as early as possible. However considering surgical and anesthetic risks, the surgery can wait until after the first 6 months of life. Unfortunately, surgical treatment does not completely prevent occurrence of melanoma from a giant congenital melanocytic nevus. Besides, several cases of melanoma occurring after blunt trauma or laser therapy have been reported. We report a case of malignant melanoma associated with a giant congenital melanocytic nevus in a 4-year-old female. The malignant melanoma occurred at the boundaries of the previous surgical excision and laser therapy sites for a giant congenital melanocytic nevus. This is the youngest case of malignant melanoma developed from a congenital melanocytic nevus in the Korean dermatological literature. (Korean J Dermatol 2011;49(12):1102~1106)