The purpose of this study, conducted in three phases, was to develop a clinically useful observational tool (i.e., the Pain Assessment Checklist for Seniors With Limited Ability to Communicate [PACSLAC]) to assess pain in seniors with severe dementia. In Phase 1, professional caregivers of seniors with severe dementia were interviewed in order to generate a list of pain-related behaviors that are characteristic of care recipients living in long-term-care facilities. Based on a systematic examination of interview transcripts by experienced researchers and an independent coder, a behavioral checklist (i.e., the initial version of the PACSLAC) was developed. The checklist items were organized into conceptually based subscales (e.g., facial expressions, activity/body movement). Phase 2 focused on an assessment of the internal consistency of the checklist (alpha =.92). Following an item analysis, the subscales of the PACSLAC (Social/Personality/Mood Indicators, Facial Expressions, Activity/Body Movement, and Physiological Indicators/Eating/Sleeping Changes/Vocal Behaviors) were found to be internally consistent. Phase 3 focused on a preliminary validation of the PACSLAC. Analyses suggest that the PACSLAC discriminated among pain events (during which there was a clear and recognizable cause for the patients' pain), events during which patients were experiencing nonpainful distress, and situations during which patients were calm.