Dermal melanocytosis is observed in various congenital conditions including nevus of Ota, nevus of Ito and Mongolian spot. It usually appears at birth or in early childhood. Several types of acquired dermal melanocytosis which usually appear in adult life have been reported. As the late onset has been stressed, the term acquired is used. We report two cases of acquired dermal melanocytosis on the forearm and the back without any similar pigmentation elsewhere on the body. The first case is a 47-year-old man who had numerous grey-blue colored macules and patches on the upper back. Histopathologic findings showed a large number of spindle-shaped cells containing melanin granules in the dermis. On electron microscopy, dermal melanocytes with stage 3, 4 melanosomes and lipid droplet were observed. The second one is a 13-year-old girl who had a 3.8 X 2.5 cm sized dark grey colored patch on the left forearm. Histopathologic and EM finding were similar to case 1. We treated both cases with topical cream(retinoid and hydroquinone), but could not observe improvement. Their lesions have persisted without any change.