This study presents the validation of the French Canadian version (PACLSAC-F) of the Pain Assessment Checklist for Seniors with Limited Ability to Communicate (PACSLAC). Unlike the published validation of the English version of the PACSLAC, which was validated retrospectively, the French version was validated prospectively. The PACSLAC-F was completed by nurses working in long-term care facilities after observing 86 seniors, with severe cognitive impairment, in calm, painful or distressing but non-painful situations. The test-retest and inter-observer reliability, the internal consistency, and the discriminent validity were found to be satisfactory. To evaluate the convergent validity with the DOLOPLUS-2 and the clinical relevance of the PACSLAC, it was also completed by nurses during their work shift, with 26 additional patients, for three days per week during a period of four weeks. These results encourage us to test the PACSLAC in a comprehensive program of pain management targeting this population.