PURPOSE To describe the proportion of long-term care (LTC) residents excluded from quality measurement because of standard length of stay inclusion criteria and the extent to which this varies across facilities. DESIGN AND METHODS A 2005 province-wide census of LTC residents’ charts was linked to additional databases from Ontario, Canada. The proportion of residents who were newly admitted (=90 days) and who exited the facility within 90 days were identified and interfacility variation in each was described. RESULTS Of the 68,930 residents in 574 facilities, 5363 (7.8%) were admitted in the prior 90 days and 7833 (11.4%) were discharged in the subsequent 90 days. Overall, 55,734 (80.4%) residents were neither admitted nor discharged within 90 days and were defined as "stable"; however, this ranged from 67.2% to 95.1% across facilities. IMPLICATIONS Stable residents are the focus of most quality measurement in LTC but transitioning residents are an important part of the caseload for these facilities. In Ontario, transitioning residents accounted for 20% of the population but there was substantial variation in this proportion across facilities. This raises concerns about the comprehensiveness and comparability of publicly reported quality indicators for a population with frequent transitions in Ontario and elsewhere.