Eight young Lemur macaco were observed in a zoo during the first 19 weeks of life. Data were obtained on general motor development, development of independence from the mother, contributions of mothers and young to the maintenance of proximity, nursing, grooming, relations between twins, play, feeding, sexual dichromatism, and communication. The results are compared with similar data from other prosimians and from anthropoid primates, and some suggestions made about the evolutionary and adaptive significance of certain aspects of L. macaco development.