Mosaicism for normal and D-trisomic cells was found in a female child whose presenting abnormalities at birth were polydactyly of the left hand and foot, hemangiomata on the forehead and lumbosacral region, slightly peculiar facies and unusual dermal patterns. Her course during the first 27 months of life was characterized by normal growth, absence of clinical evidence of congenital heart disease, moderate developmental retardation, tonguetie and toe-walking. Trisomic cells were more numerous than normal cells in skin cultures, whereas the reverse was true for peripheral leukocytes.