This project compared the temperament of very low birth weight (VLBW) infants to that of full-term infants at 6 and 12 months of age, assessed patterns of change in temperament from 6 to 12 months, and investigated effects of the neonatal experience on manifestations of temperament in VLBW babies. The subjects were 41 VLBW infants who were free of congenital anomalies and appropriate for gestational age. Instruments included the Infant Temperament Questionnaire (ITQ), Toddler Temperament Questionnaire (TTQ), and the Home Observation for Measurement of the Environment (HOME) Inventory. At 6 months, the VLBW infants were significantly less adaptable and more intense than full-term infants. There were significantly more "difficult" and fewer "easy" infants in the study group. At 12 months, the infants were less persistent than a full-term toddler. Behavioral style clusters of the toddlers did not differ significantly from published data. Multiple regression analyses revealed that the social environment of the VLBW infant plays an important role in the manifestation of childhood temperament as early as 6 months of age. Results suggest that VLBW infants do manifest behavioral styles that are different from full-term infants but are modified during the first year of life. In addition, the nine temperament dimensions were differentially affected by adverse perinatal events and environmental factors.