The clinical and histologic spectrum of melanotic macule of the nail unit is examined and the differences in the clinical appearance of longitudinal melanochychia caused by melanotic macule and by other kinds of proliferations of melanocytes are assessed. We observed that the clinical appearance of the pigmented band was of little help in establishing the underlying basic pathologic process. This underscores the importance of obtaining a biopsy of the nail matrix in patients who present with solitary longitudinal melanonychia.