We studied whether there exist variations in pain responses between different intellectual and developmental disability (IDD) etiologies. Self-reports and facial expressions (Facial Action Coding System = FACS) were recorded during experimental pressure stimuli and compared among 31 individuals with IDD--13 with cerebral palsy (CP), nine with Down syndrome (DS), nine with unspecified origin (UIDD)--and among 15 typically developing controls (TDCs). The CP and DS groups had higher pain ratings and FACS scores compared to the UIDD and TDC groups, and steeper stimulus-response functions. The DS group exhibited the most diverse facial expressions. There were variations in the foci of facial expressions between groups. It appears that different IDD etiologies display distinct pain responses.