BackgroundTobacco smoking is a health care issue in developed as well as in developing countries. Tobacco smoking among people with mental illness is significantly higher than in the general population. Tobacco smoking has negative effects on physical, mental and financial well-being of people with mental illness but little is known about tobacco dependence among mental health service users in sub-Saharan African countries, including Ethiopia. Therefore, this study attempted to assess the prevalence of tobacco dependence and associated factors among mental health service users at Jimma University teaching hospital.MethodsA cross-sectional study was conducted among 305 male and 117 female mental health service users at Jimma University teaching Hospital in 2014. The Fagerstrom Test for Nicotine Dependence (FTND) was used to assess tobacco dependence. Logistic regression analysis was used for bivariate and multivariate analysis. Variables with a P value of <0.05 were considered to be associated with tobacco dependence in the final model.ResultsThe prevalence of current tobacco dependence among the study participants was 18.5%. Amongst people with tobacco dependence, 57.7, 29.5 and 12.8% had moderate, high and very high level of tobacco dependence respectively. All mental health service users with tobacco dependence were males. There was a significant association between tobacco dependence and high school education (AOR 3.02, 95% CI 1.07, 8. 48), alcohol use disorder (AOR 4.14, 95% CI = 1.54, 11.11), daily khat chewing (AOR 13.51, 95% CI = 4.27, 42.74), chewing khat 2–3 times per week (AOR 5.09, 95% CI = 1.37,18.95), chewing khat once a week (AOR 4.31, 95%CI = 1.04,17.78), having friends who smoke tobacco (AOR 4.88, 95% CI = 2.12, 11.25) and being diagnosed with schizophrenia compared to a diagnosis of major depression (AOR 5.26, 95% CI = 2.07, 13.37). However, daily attendance at a place of worship (AOR 0.46, 95% CI = 0.22, 0.95) was associated negatively with tobacco dependence.ConclusionIn this study, there was a high prevalence of tobacco dependence among mental health services users. There is a pressing need to increase availability of psychological and pharmacological interventions to reduce tobacco dependence and tobacco-related medical illness in this vulnerable group.