The purpose of this study is to describe facial, behavioral and physiologic (heart rate) reactivity of children with autism aged 3 to 6 years old, during a painful stimulation (venepuncture). Children will be videotaped before, during and after a venepuncture. Each recording will be rated with the FACS (Facial Action Coding System) and the NCCPC (Non Communicating Children's Pain Checklist).