Despite the adoption of strategies to prevent and treat multidrug-resistant tuberculosis (MDR-TB) over the past decade, Latvia continues to have one of the highest rates of MDR-TB in the world. It is important to identify modifiable factors that may impact on MDR-TB patient outcomes. A study was conducted to elucidate the association between nutritional status and clinical presentation, clinical course, and mortality in 995 adult patients treated for MDR-TB from 2000 to 2004. Twenty percent of patients were underweight, defined as a body mass index <18·5, at the time of diagnosis. These patients were significantly more likely to have clinical evidence of advanced disease, and had a greater risk of experiencing ⩾3 side-effects [adjusted odds ratio 1·5, 95% confidence interval (CI) 1·1–2·1] and death (adjusted hazard ratio 1·9, 95% CI 1·1–3·5) compared to patients who were normal or overweight. Interventions aimed at these high-risk patients, including nutritional supplementation as an adjunct to anti-TB therapy, should be considered and evaluated by TB programmes.