Tuberculosis (TB) and malnutrition co-exist. Malnutrition predisposes to development of TB, and may further predict treatment outcomes. Given the paucity of data regarding malnutrition in specific populations with multidrugresistant (MDR)-TB, we aimed to determine the pre-treatment and post-treatment change in nutrition status, as measured by body mass index (BMI), in patients from Tanzania initiating MDR-TB treatment, as well as potentially modifiable determinants of BMI in this population at high-risk for treatment failure.Design: A retrospective cohort was followed consisting of patients admitted for MDRTB treatment at Kibong'oto National MDR-TB Center of Excellence, the national referral hospital for all cases in Tanzania.Results: Of 104 MDR-TB cases admitted from November 2013 through June 2014, 96 (92%) cases were assessed for nutrition status. Fifty-one (53%) were malnourished, of which 15 (30%), 15 (30%) and 21 (45%) were classified as mild (BMI <18.5 -17), moderate (BMI <17 ≥ 16) and severe (BMI <16) respectively. Gender, HIV status, and pre-treatment CD4 count among those HIV infected did not influence pre-treatment nutrition status. Thirty-seven (39%) of MDR-TB patients improved grades (e.g. from severe to moderate malnutrition) and gained a mean BMI of 2 kg/m 2 (95% CI: 1-3), yet 9 (9%) deteriorated grades and thus developed acute adult malnutrition during treatment. In those that developed acute malnutrition during treatment, the mean lost BMI was 3 kg/m 2 (95% CI; 0.3-8). Categorical change in BMI grade trended toward association with the duration of inpatient admission (p=0.05). Conclusion:Malnutrition is a common comorbidity in MDR-TB patients receiving treatment in Tanzania. Importantly, some MDR-TB patients while on treatment developed acute malnutrition. Given the lack of predictors of developing malnutrition, these findings suggest the need for frequent assessment of nutrition status during the course of MDR-TB treatment, to identify patients that may require additional therapeutic supplements.