The role of pain in relation to self-injurious behavior (SIB) among individuals with intellectual disabilities is not well understood. Some models of SIB are based on altered endogenous opioid system activity which could result in elevated pain thresholds. In this study, non-verbal behavioral signs indicative of pain as measured by the Non-Communicating Children's Pain Checklist (NCCPC) were compared between matched individuals with (N=35) and without (N=35) chronic self-injurious behavior (SIB) and neurodevelopmental disorders. Significant (p less than 0.01) between group differences (SIB Group greater than Control Group) were found for the NCCPC Total Score, and for the Vocal, Social/Personality, and Eating/Sleeping subscales of the NCCPC. These results are not consistent with models of SIB in which pain sensitivity is assumed to be attenuated because of opioid system activity and are suggestive of intact and possibly amplified pain expression. (Contains 2 figures.)