Universal dyschromatosis is a generalized leucomelanodermia recognised in Japan in 1933. We report a family with universal dyschromatosis, demonstrating the mode of transmission. The ultrastructural aspects are compatible with a functional melanogenesis anomaly.A 9-year-old girl was hospitalized for recently diagnosed insulin-dependent diabetes mellitus. She was born to non-consanguinous parents and her past medical history was uneventful. Her father was of mixed ethnic origin. The physical examination revealed generalized leukomelanoderma identified since the first year of life. Zones of small achromatic maculae alternated with zones of pigmented maculae of variable size and color. Lesions were diffuse but predominated on the trunk and did not involve the face, the hands or the feet. Neither the child nor her father who also has leukomelanoderma were photosensitive. A skin biopsy from the gluteal region revealed alternating zones of hyper- and hypopigmentation. The ultrastructural analysis showed that the number of melanocytes was not significantly different in the different pigmented zones and the pigment transfer to adjacent keratinocytes was intact. There were three other girls in the kinhood and two, as well as a few other individuals in the family, had a localized form of the disease.Universal dyschromatosis is a rare genodermatosis. The familial cases reported here illustrate the variable clinical presentations of this pigmentary abnormality. The pedigree in this family demonstrated incomplete penetrance of hereditary leukomelanoderma with autosomal dominant inheritance. The localized forms reported to date under different names would actually appear to correspond to incomplete expression of the dermatosis. The skin manifestations in universal dyschromatosis would appear to be similar to those in a few other skin diseases, mainly xeroderma pigmentosum, especially the localized forms; for generalized forms however, there is little room for confusion as photosensitivity is absent and lesions predominate in unexposed zones. The ultrastructure investigations showed different levels of melanocyte activity without abnormal pigment production or transfer. This abnormality has variable expression, explaining the multitude of clinical presentations.