This study examined the relation of negative emotionality in infancy to child social and cognitive developmental outcomes among low birth weight (LBW) preterm infants participating in the Infant Health and Development Program (IHDP), a comprehensive compensatory education intervention beginning in infancy and lasting through age 3 years. In this analysis, intervention effects at age 36 months on maternal report of child behavior as assessed by the Child Behavior Checklist externalizing and internalizing scales and on intelligence as measured by the Stanford-Binet scale were largest among children characterized by higher levels of negative emotionality in infancy. Findings indicate that for LBW preterm infants characterized by negative emotionality at age 12 months the intervention was associated with a twofold decrease in the occurrence of clinically meaningful levels of behavior problems at age 3 years and a fourfold decrease in the occurrence of a high-risk profile in which both internalizing and externalizing scores are in the clinically meaningful range. The intervention was also associated with a fivefold decrease in the occurrence of IQ < or = 75 at age 3 years among children with higher levels of negative emotionality and heavier LBW (2001-2500 g). However, specific aspects of temperamental difficulty such as fearfulness and anger were related to internalizing and externalizing, respectively, in both the intervention and control groups. Findings are consistent with research linking negative emotionality in infancy with social and cognitive developmental outcomes in early childhood among normal birth weight infants. Results suggest the need for further attention to child temperament in early intervention research.