Four patients with Prader-Willi syndrome, diagnosed in the neonatal period and followed during the first year of life, are reported. There were three males and one female. All four patients presented with hypotonia and distinct craniofacial dysmorphism. Prometaphase chromosome analysis showed interstitial deletion of 15q in all of them. The placentae and umbilical cords were examined in three of the patients and found normal. Electromyography done in the neonatal period suggested primary myopathy. Height, weight and head circumference were normal at birth in all patients. Hand and foot measurements showed normal size at birth and during the first year of life.