BACKGROUND: Northwest Syria accounts for over 4 million people of whom more than half are internally displaced persons (IDPs). More than 1 million IDPs reside in camps and many more live in settings which are overcrowded and poorly ventilated. Suboptimal social living conditions leave these populations susceptible to tuberculosis (TB) morbidity and mortality. This study aimed to assess the effect of internal displacement due to armed conflict on the risk of unsuccessful treatment outcomes among TB patients in northwest Syria. METHODS: All patients registered to start TB treatment at three centres in northwest Syria between the 1st June 2019 to the 31st December 2020 were included. Unsuccessful TB treatment outcome was defined as a composite outcome combining the WHO TB treatment outcomes of treatment failure, loss to follow-up, and death. We assessed the association between internal displacement and unsuccessful TB treatment outcomes using multivariable logistic regression. We also explored the risk of an unsuccessful treatment outcome by internal displacement setting (camp, village or city). RESULTS: Of the total 737 registered patients included in the analysis, 400 (54%) were documented as internally displaced. The median age of IDPs was 30 (IQR: 21.5-48) and the median age of residents was 34 (IQR:22-50). A significantly higher percentage of those who were IDPs had an unsuccessful treatment outcome compared to residents (40% vs 18%, p<0.001). After adjustment for confounders, the relative risk of having unsuccessful TB treatment was two-fold higher in internally displaced TB patients compared to residents (95% CI: 1.5-2.6). IDPs living in villages had a 30% lower risk of an unsuccessful treatment outcome compared to IDPs living in camps (RR 95% CI: 0.50-0.91), and IDPs living in cities had a 13% lower risk of an unsuccessful treatment outcome (RR 95% CI: 0.57-1.18). CONCLUSION: This is one of few studies which aims to quantify the effect of internal displacement on TB treatment outcomes during times of conflict. Our findings starkly highlight how social determinants contribute to poor TB outcomes and act as a starting point for much needed research on how best to manage TB in humanitarian crisis settings.