A retrospective study of 16 patients identifying physical features of neonates with Prader-Willi syndrome is reported from the Department of Pediatrics, Division of Genetics, William Beaumont Hospital, Royal Oak, MI and Section of Genetics, Department of Pediatrics, University of Arizona, Tucson. Medical records of 16 patients observed in the clinic at the University of Connecticut Health Center, Farmington, were reviewed for descriptions made during the newborn period. At the time of the chart review the patients ranged in age from eight months to 33 years. All initial examinations were performed at 22 days of age or earlier. Of 13 patients with high resolution chromosome analysis 12 showed the typical deletion of the long arm of chromosome 15. Several of the characteristic features of Prader-Willi syndrome in early infancy were confirmed including hypotonia and genital hypoplasia. Features that have not previously been emphasized included an abnormal cry, disproportionately large head circumference and anterior fontanel, mild micrognathia, mild anomalies of gingivae or alveolar ridges, and changes in the appearance of the skin such as poor color, cyanosis, jaundice, ecchymoses, hirsutism, and foot edema. Hypoplasia of the scrotum was present with a normal appearing penis. Contrary to one previous report the hypotonia was associated with absence of deep tendon reflexes, and hyperreflexia was found in only one. [1]