The present study investigated the relationship between infant temperament characteristics and autism spectrum disorder (ASD) risk status. Temperament was examined at 6, 12, and 24�months in 282 infants at high familial risk for ASD and 114 low-risk controls using the Infant Behavior Questionnaire-Revised and Early Childhood Behavior Questionnaire. Infants were divided into three groups at 24�months: High-Risk Positive—classified as ASD (HR Pos), High-Risk Negative (HR Neg), and Low-Risk Negative (LR Neg). At 6 and 12�months HR Pos infants exhibited lower Surgency and Regulatory Capacity than LR Neg infants. By 12�months they also demonstrated increased Negative Affect. Group differences remained, when early signs of ASD were controlled for, suggesting that temperament differences could be useful targets for understanding the development of ASD.