[영문]BACKGROUND:: Emergency department (ED) use in Quebec may be measured from varied sources, eg, patient's self-reports, hospital medical charts, and provincial health insurance claims databases. Determining the relative validity of each source is complicated because none is a gold standard. OBJECTIVE:: We sought to compare the validity of different measures of ED use without arbitrarily assuming one is perfect. SUBJECTS:: Data were obtained from a nursing liaison intervention study for frail seniors visiting EDs at 4 university-affiliated hospitals in Montreal. MEASURES:: The number of ED visits during 2 consecutive follow-up periods of 1 and 4 months after baseline was obtained from patient interviews, from medical charts of participating hospitals, and from the provincial health insurance claims database. METHODS:: Latent class analysis was used to estimate the validity of each source. The impact of the following covariates on validity was evaluated: hospital visited, patient's demographic/clinical characteristics, risk of functional decline, nursing liaison intervention, duration of recall, previous ED use, and previous hospitalization. RESULTS:: The patient's self-report was found to be the least accurate (sensitivity: 70%, specificity: 88%). Claims databases had the greatest validity, especially after defining claims made on consecutive days as part of the same ED visit (sensitivity: 98%, specificity: 98%). The validity of the medical chart was intermediate. Lower sensitivity (or under-reporting) on the self-report appeared to be associated with higher age, low comorbidity and shorter length of recall. CONCLUSION:: The claims database is the most valid method of measuring ED use among seniors in Quebec compared with hospital medical charts and patient-reported use.