The dearth of information on the pain experience of individuals with intellectual and developmental disabilities (IDD) calls for a more comprehensive understanding of pain in this population. The Non-Communicating Adults Pain Checklist (NCAPC) is an 18-item behavioral scale that was recently found to be reliable, valid, sensitive and clinically feasible to assess pain levels in adults with IDD. The aim of the present article is to propose and examine a pain model for adults with IDD. The procedure involved videotaping 228 participants (mean age: 38.7 years) before and during an influenza vaccination. The pain model was constructed using previously collected data, by means of confirmatory factor analysis of the sum scores, using the half split procedure. The model was tested on a randomized group of participants (N = 89) for generalization. The constructed model seems to reflect two categories of pain responses: a basic response consisting of physiological measures and body reaction, and an advanced response consisting of vocal and emotional reactions, as well as facial and protective expressions. The model presented excellent Goodness of Fit Index (0.99) and an acceptable RMSEA value (0.061). We conclude that the current article presents a first-of-its-kind model of pain behavior in adults with IDD. (Contains 2 figures and 2 tables.)