SETTING: The three Basic Management Units (BMUs) of the National Tuberculosis Programme (NTP) in Cotonou, Benin. OBJECTIVE: To determine the prevalence of diabetes mellitus (DM) among tuberculosis (TB) patients in Cotonou. DESIGN: A cross-sectional study of consecutively registered TB patients treated for a minimum of 2 weeks between June and July 2014 in the three BMUs, with measurement of their fasting blood glucose (FBG). A patient was considered as having DM if venous FBG was ⩾7 mmol/l or if they reported a known history of DM. RESULT: There were 159 patients assessed: 114 with new smear-positive pulmonary tuberculosis (PTB), 5 with new smear-negative PTB, 8 with extra-pulmonary TB, 21 retreatment patients with fully susceptible bacilli and 11 with multidrug-resistant TB. Of these, respectively 31 (19%), 18 (11%) and 10 (6%) were human immunodeficiency virus co-infected, smokers and hypertensive. Eight patients (5%) had impaired fasting glucose and three (1.9%) had DM (FBG ⩾ 7 mmol/l), of whom two were already known to have the disease and one was newly diagnosed. CONCLUSION: DM may not be an important risk factor for TB in Cotonou. A larger study on TB and DM in the whole country is needed.