There is a lack of knowledge about pain reactions in children with autism spectrum disorders (ASD), who have often been considered as insensitive to pain. The objective of this study was to describe the facial, behavioral and physiological reactions of children with ASD during venipuncture and to compare them to the reactions of children with an intellectual disability and nonimpaired control children. We also examined the relation between developmental age and pain reactions. The sample included 35 children with ASD, 32 children with an intellectual disability, and 36 nonimpaired children. The children were videotaped during venipuncture and their heart rate was recorded. Facial reactions were assessed using the Child Facial Coding System (CFCS) and behavioral reactions were scored using the Noncommunicating Children’s Pain Checklist (NCCPC). A linear mixed-effects model showed that children’s reactions increased between baseline and venipuncture and decreased between the end of venipuncture and the recovery period. There was no significant difference between groups regarding the amount of facial, behavioral and physiological reactions. However, behavioral reactions seemed to remain high in children with ASD after the end of the venipuncture, in contrast with children in the 2 other groups. Moreover, we observed a significant decrease in pain expression with age in nonimpaired children, but no such effect was found regarding children with ASD. The data reveal that children with ASD displayed a significant pain reaction in this situation and tend to recover more slowly after the painful experience. Improvement in pain assessment and management in this population is necessary.