Chromosome studies were made on a 2-month-old boy with multiple congenital anomalies including an elongated large head, capillary hemangiomas, hypertelorism, bilateral cleft lip and cleft palate, overlapping fingers, and an undescended testis. Lymphocyte cultures revealed 46 chromosomes with a minute Y chromosome with deletion of most of the long arm; however, there was mosaicism in fibroblast cultures with a 45,XO/46,XYq- pattern. The parents' karyotypes were normal, and the Y chromosome of the father was of normal size with characteristic bright fluorescence pattern.