Nail (subungual) melanoma is a rare subtype of acral lentiginous melanoma that arises in the nail unit due to malignant melanocytic hyperplasia in the nail apparatus. Nail apparatus melanoma is a more frequently represented melanoma in darker skin phototypes, such as individuals of African (15%-20% of all melanomas), American Indian (33%), Hispanic, and Asian (10%-30%) descent, than in individuals of Northern European descent (1%-3%). The diagnosis is challenging and often delayed (average depth at the time of diagnosis is 3.5-4.7 mm). Therefore, it can carry significant mortality and morbidity.

The vast majority of nail melanomas arise in the nail matrix. Melanoma arising from the nail bed is rare. Two-thirds of cases of nail melanoma present as longitudinal melanonychia. More advanced cases present as a subungual mass with associated onychodystrophy. Hutchinson's sign (extension of pigment to the nail folds) is another sign of advanced nail melanoma. Some subungual melanoma cases are amelanotic (nonpigmented), making early diagnosis even more difficult.

The thumb is the most frequently involved digit, followed by the hallux and then index finger. Subungual melanoma most commonly affects adults in the fifth to seventh decades. There is no male or female predilection.

Nail melanoma is exceedingly rare in children. The majority of pediatric cases occur in children with darker skin phototypes. Similar to their adult counterparts, pediatric cases often present as longitudinal melanonychia.