Int. J. Environ. Res. Public Health 2011, 8 257 Dryden were included in the Northwestern Public Health District, and Thunder Bay, Nipigon, Geraldton, Terrace Bay, Marathon, and Manitouwadge were included in the Thunder Bay Public Health District. 3. Results and Discussion The screening and tobacco use outcomes are presented in Table 1. The total number of ED visits averaged 136,338/year. When each patient’s first visit each year was used to censor the data, approximately 50% of records were excluded for the tobacco use prevalence analyses for each year of the study (Table 1). Tobacco screening rates were consistent across all four years (85–89%) and between the community hospitals and the regional hospital. Among patients screened for tobacco use, 48% were male, the average age was 46  19, and 69% of all visits were accounted for by patients less than 55 years of age. Overall tobacco use remained relatively stable across the years (26–27%) with the only discrepancy being higher rates in 2007 (32%; Table 1). Although the overall tobacco use rates are high compared to the 18% provincial and national averages [7], they are consistent with overall regional averages for the general population which are the highest in the province [13], likely due, at least in part, to a large blue collar population (mining, logging, and pulp/paper mills), lower socio-economic status compared to provincial averages, and a large First Nations population [10] all of which are associated with higher smoking rates [14-16]. Showing tobacco use prevalence in the 5-year age categories chosen for this study helped to define exactly where tobacco use prevalence decreased by age (Table 1 and Figure 1). These data are unique—although population data show that prevalence rates decrease with age, most published tables have an age ceiling of 45+, 55+, or 65+ and use larger groupings than 5-years and thus do not clearly show where the threshold for change in prevalence lies. The current findings show that tobacco use prevalence remained over 30% for each five-year age group until age 50 (36% overall for patients <50 years). Prevalence decreased to 26% for patients in their 50’s, decreased to 16% for patients in their 60’s, and decreased substantially to 5% for patients 70+ years. Follow-up analyses showed that the decrease in tobacco prevalence from 2007 to 2008 was due to a 1% decrease in the community hospitals (owing to a drop from 43% to 42% among patients <50 years) and an 8% decrease in the regional hospital, which was most pronounced for patients <70 years of age—10% decrease among patients <50 years (41% to 31%), 6% decrease for 50–69 years (25% to 19%), and 2% decrease for 70+ years (6% to 4%; Figure 1). There is no clear explanation for the dramatic drop in prevalence at the regional hospital from 2007 to 2008—there were no new community-level smoking cessation initiatives, municipal smoking bylaw changes, or tobacco cost changes that were different in the urban centre versus the rural communities, and no identifiable changes at the regional hospital that could have been responsible for a change in patient population such as fewer visits from people living outside of Thunder Bay in the rural communities. Although it is possible that the 2007 decrease was a systems error at the regional hospital, it is unlikely because the overall number of ED visits, the proportion of visits by age group, the proportion of patients asked about tobacco status, and the overall pattern of tobacco use by age group remained the same from 2007–2008.