"Longitudinal melanonychia" refers to a brown or brown-black longitudinal band on a fingernail or toenail. A number of conditions can cause longitudinal melanonychia, but its main importance is that, in some patients, it may indicate the presence of a subungual malignant melanoma. Hyperpigmented nail bands are not uncommon in African-American, Latino and Asian patients, especially those over sixty years of age, and are often multiple in these groups. Longitudinal melanonychia is most worrisome when there is a solitary, dark, broad longitudinal band with pigment extending over the proximal nail fold (Hutchinson's sign). Such findings are considered to be a strong indication for biopsy of the nail matrix to rule out melanoma. Since nail matrix biopsy sometimes results in permanent nail deformity, and since the incidence of malignant melanoma is quite small in the pediatric age group, there is some controversy as to whether this procedure should routinely be performed in children. We report two cases of dramatic longitudinal melanonychia in toddlers and review the current literature on the management of this striking condition in the pediatric age group.