We report 6 malignant melanomas of the nail apparatus in situ. All cases showed melanonychia striata extended over whole nail with the periungual pigmentation (Hutchinson's sign) clinically. Proliferations of atypical melanocytes were seen limited in epidermis histopathologically. The nail surface profiles by dermatoscope were composed of linear pigmentation, whereas the periungual pigmentation showed diffuse irregularly shaped pigmentation distributed in a disorderly fashion as well as acral lentiginous melanomas in situ. In contrast, both the ungual and the periungual surface profiles of pigmented nevi showed longitudinal linear pigmentation. These distinctive features of surface profiles are very helpful for the differential diagnosis of the longitudinal melanonychia striata with the periungual pigmentation.
