This study investigated the ability of the Neonatal Behavioral Assessment Scale (NBAS), in combination with neonatal histories and developmental assessments, to predict mental and motor performance of 9-month-old infants on the Bayley Scales of Infant Development (BSID). Fourteen normal, full-term infants and 10 average-for-gestational-age, pre-term infants were studied. In all cases the NBAS assessments were completed when the infants were 40, 42, and 44 weeks gestational age. The BSID assessments were completed at 2, 4, 6, and 9 months gestational and chronological age for all infants. Also recorded at birth for all infants were Apgar scores, height and head circumference. Size and social-economic status of the family and birth order of the child were obtained via standard hospital procedures. Discriminate analysis yielded 100% of 9 month performance and pre-term or full-term group membership. NBAS subscales and neonatal histories provided three of four predictors of normal function and 11 of 11 predictors of abnormal function. (Author/SS)