What this study adds. This large retrospective cohort study of over 3,100 patients in Yaoundé reveals that smear non-converters (10.6% of the cohort) who received an extended intensive phase had significantly worse outcomes. Their favorable outcome rate was 79.1%, compared to 90.6% for converters. They were also over twice as likely to be lost to follow-up and nine times more likely to experience treatment failure. Implications for practice, policy, or future research. Simply extending therapy is insufficient for smear non-converters. Programmatic measures must intensify for this group, including active tracing to prevent loss to follow-up, prompt drug susceptibility testing to exclude resistance, and consideration of more individualized treatment regimens to address the underlying causes of delayed conversion. This publication is available in full in Health Research in Africa.