Objective To investigate differences in neurobehavior between preterm infants at term and full-term infants, changes in neurobehavior between 34 weeks postmenstrual age (PMA) and term equivalent in the preterm infant, and the relationship of neurobehavior to perinatal exposures. Study design In this prospective cohort study, 75 infants were tested at 34 weeks PMA and again at term using the Neonatal Intensive Care Unit Network Neurobehavioral Scale. Infants underwent magnetic resonance imaging at term equivalent. Regression was used to investigate differences in the scale's domains of function across time and in relation to perinatal exposures. Results At term equivalent, preterm infants exhibited altered behavior compared with full-term infants, with poorer orientation (P < .001), lower tolerance of handling (P < .001), lower self-regulation (P < .001), poorer reflexes (P < .001), more stress (P < .001), hypertonicity (P < .001), hypotonia (P < .001), and more excitability (P = .007). Preterm infants from 34 weeks PMA to term equivalent, demonstrated changes in motor functions with declining quality of movement (P = .006), increasing hypertonia (P < .001), decreasing hypotonia (P = .001), and changes in behavior with increasing arousal (P < .001), increasing excitability (P < .001), and decreasing lethargy (P < .001). Cerebral injury was associated with more excitability (P = .002). However, no associations were detected between any of the perinatal exposures and developmental change from 34 weeks PMA to term equivalent. Conclusion Preterm infants have altered neurobehavior in a broad number of domains at term equivalent. Cerebral injury alters neurobehavior but does not appear to impair early neurobehavioral changes. Important neurobehavioral changes occur before term, and this provides an opportunity for interventions in the neonatal intensive care unit.