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To examine the pattern of tuberculosis (TB) occurring among immigrants and the interval from arrival in Canada to diagnosis of the disease.Study of all cases of TB diagnosed in foreign-born residents of southern Alberta during the 5-year period 1990-1994.A centre for the diagnosis, management and control of all cases of TB in the southern half of the province of Alberta.All foreign-born patients in whom TB was newly diagnosed between January 1990 and December 1994 were included in the study. The interval from their arrival in Canada to diagnosis, their country of birth and the site of their disease were documented.Immigrants to Canada accounted for 248 (70.6%) of the 351 cases of TB diagnosed in southern Alberta during the 5-year period. The majority of these immigrants (182/248 [73.4%]) were of Asian origin. Extrapulmonary TB accounted for 111 (61.0%) of the 182 cases of the disease in Asian immigrants. The mean period between immigration and diagnosis was 11.2 years (standard deviation [SD] 13.9 years). Half of the patients presented within 7 years of their arrival in Canada. The time to presentation was shortest for patients with superficial lymph node disease (mean 7.6 years [SD 6.9] after arrival), intermediate among those with extrapulmonary disease, excluding superficial disease of the lymph node (10.1 years [SD 12.1]), and longest for those with pulmonary disease (14.2 years [SD 17.2]). TB developed sooner after arrival in Canada among immigrants from Asian countries (mean 9.1 years) than among those from other countries (17.2 years) (p = 0.01).Given the low annual incidence of TB in Canada (7.1 per 100 000), it is probable that TB occurring among immigrants reflects infection acquired before arrival in Canada. Health care professionals need to be aware that immigrants from countries with a relatively high prevalence of TB remain at risk for the disease (often at an extrapulmonary site) for many years after they immigrate to low-prevalence countries.