Background: Shorter treatment regimens have been shown to improve treatment outcomes in several observational studies. STREAM Stage 1, a multi-country non-inferiority randomised trial, compared a 9-month regimen with the longer WHO regimen showing comparable success rates. We investigated baseline factors predictive of long-term TB-related outcomes in patients who received the short regimen. Design/Methods: Baseline demographics, clinical/laboratory, bacteriological and radiological characteristics were collected and all participants in the modified intention to treat population were followed up to 132 weeks post-randomisation. Participants were classified as definitely or probably experiencing a failure or relapse event (FoR) using data up to the time they reached the trial primary endpoint. Baseline variables that were found to be significantly associated (p<0.1) with FoR in univariable analysis were assessed in a multivariable Cox regression model (backwards elimination, exit probability p=0.05) to identify factors that were independently associated with FoR. Results: On the short regimen, 25 (9.9%) out of 253 participants were classified as FoR; the probability of FoR by week 132 was estimated as 0.11 (95% CI 0.07,0.15). Sex, smoking status, baseline smear grade, extent of opacities, cavitation, and presence of costophrenic obliteration were significantly associated with an unfavorable outcome (all p<0.1). Male sex, higher smear grade, HIV co-infection, and obliteration of costophrenic angle remained independently associated in multivariable analysis (all p<0.05). These four factors remained independently associated when week 8 culture was included in the multivariable analysis and there was borderline evidence that a positive culture at week 8 was predictive of FoR (p=0.052). Conclusions: There is evidence to suggest that male gender, HIV status, and high grade smears may be associated with a higher risk of failure or relapse. Novel strategies that target patients with high-risk baseline characteristics are needed. The association of costophrenic obliteration with a worse outcome is most likely an incidental finding