Chronic Lung Disease (CLD) is associated with a higher risk of developmental disabilities, including mental retardation and cerebral palsy. The current study assessed the effect of severe CLD on classroom peer adjustment and parent-reported behavior problems in 8-year-old children recovered from CLD. Twenty-four infants with neonatal CLD were prospectively enrolled, along with 26 controls who were similar in birth weight, gender, and maternal education. Infants in each group had birth weight <1500 grams, no major anomaly, and required assisted ventilation in the neonatal period. Infants in the CLD group had the same attributes and, in addition required supplemental oxygen at 36 weeks post-conceptional age. As part of an ongoing, longitudinal follow-up study of high-risk nursery graduates at 8 years of age, parents, teachers and children participated in a comprehensive follow-up clinic designed to assess medical, psychological, educational, and social development. Part of this assessment included completion of the Conners' Parent Rating Scale and Child Behavior Checklist. The child's teacher was surveyed about social and academic success. Teachers were not informed of students' past medical history. Forty percent of the children recovered from CLD were rated by their teachers as having unsatisfactory peer adjustment, compared with 6 percent of control children (Chi square = 5.8, p=<.01). Parents reported more behavior problems among the children who had CLD in the areas of aggression, attention, social difficulties, and somatic complaints on the CBCL, and in the domains of impulsivity-hyperactivity and learning difficulties on the Conners Scale (all p <.01). Neonatal CLD appears to be associated with long-term effects on behavior and socialization. Several studies have reported cognitive and academic deficiencies associated with prematurity and CLD, and differences appear to extend to other areas of function as well. While a few previous studies have linked prematurity to later behavior problems, none have investigated specific medical complications of prematurity and their possible association with behavioral-social problems. It will be important to elucidate the effects of such factors in order to improve anticipatory counseling and screening by neonatologists and other health care professionals.