Two cases of diffuse congenital melanosis are presented. The hyperpigmentation appeared shortly after birth and invades progressively the trunk and the limbs. It is diffuse and most intensive on the abdomen and the back, and reticulated on the neck, the genitals and in the groins. The nails are thin and their surface is slightly irregular. Histologic examination reveals the presence of melanin in the deep and superficial layers of the epidermis. On electron microscopy the melanosomes are not grouped within the keratinocytes, but are dispersed throughout the cytoplasm of the epidermal cells. The disease can be considered as an autonomous entity. The mechanism of the hyperpigmentation is not known.