The present study investigated whether the Brazelton Neonatal Assessment Scale predicts 10-week performance on the Bayley Scales of Infant Development and examined whether early temperament relates to performance on both scales. 18 normal, term infants were studied. Conceptual, a priori scoring dimensions were applied to neonatal assessments at a mean of 8.6 days. Infant temperament data were available for 12 of the subjects at a mean of 13.3 days, and mental and motor development were assessed for all subjects at a mean of 68.8 days. The results indicate that the total of a priori Brazelton scoring dimensions and neonatal state control were predictive of Bayley mental quotients at 10 weeks. Caretakers' judgments of temperamental intensity and distractability at 2 weeks correlated with the Bayley scales and the Brazelton dimensions. Furthermore, dividing the infants into worrisome and optimal groups on the basis of the total produced significant differences in Bayley mental scores.