Background: Neurodevelopmental disabilities in children with congenital heart defects (CHDs) have been primarily attributed to intraoperative events without consideration of preoperative and postoperative factors. Objective: To describe the preoperative and postoperative neurodevelopmental status of newborns and infants with CHDs. Study design: One hundred thirty-one children (56 newborns and 75 infants) were evaluated before and after surgery by using standardized neurobehavioral (newborn) and motor assessments (infant) and neurologic examinations. Results: In newborns, neurobehavioral abnormalities were documented in >50% before surgery, with abnormalities persisting in most after surgery. In infants, neurodevelopmental abnormalities were observed in 38% before surgery. There was a significant association between preoperative and postoperative neurodevelopmental status, with status remaining unchanged in most. Newborns with acyanotic heart lesions were more likely to demonstrate neurologic compromise than those with cyanotic defects. For infants, arterial oxygen saturations <85% were significantly associated with an abnormality. There was a trend for a longer circulatory arrest time to be associated with greater risk for neurologic sequelae in newborns, whereas prolonged cardiopulmonary bypass was an important risk factor for infants. Conclusions: Neurodevelopmental abnormalities are common in young infants with CHDs and are often present before open heart surgery. These developmental concerns are clinically underappreciated. Early systematic developmental screening may be warranted in this population of interest. (J Pediatr 2000;137:638-45)