A six-pound infant may be 33 weeks, 43 weeks, or term, each with a different set of medical and developmental needs, requiring different nursing care. Gestational age determination is important for anticipating each infant's medical risks, preventing complications, distinguishing the infant's developmental capabilities in feeding, sleep, and interactive behaviors with the parents, and establishing the infant's nursing care needs on a timely basis. This article reviews the history of gestational age assessment, gestational age classifications and associated risks, and the accuracy of current tools and provides instruction for performing a gestational age assessment.