Setting: Papua New Guinea (PNG), a low-resource country with a high tuberculosis (TB) burden. Objective: To describe the characteristics, treatment outcomes and risk factors for unfavourable outcomes among patients registered for first-line tuberculosis (TB) treatment between 1 January 2014 and 31 December 2016 in West Sepik Province. Design: This was a retrospective cohort study of routinely collected programme data. Results: Of 1058 cases, 50.7% were male and 38.8% were aged <15 years; 43.1% were extrapulmonary TB cases and 280 (26.5%) were bacteriologically confirmed. No human immunodeficiency virus (HIV) status was recorded for 74.7% of cases. Of 1019 (96.3%) patients with a recorded outcome, 779 (76.4%) were favourable and 240 (23.6%) were unfavourable. On multivariable logistic regression, increasing age was associated with an increased odds of an unfavourable outcome (adjusted OR [aOR] 1.06 per every 5-year increase, 95%CI 1.02–1.11; P = 0.006) and being a retreatment case was associated with a reduced odds of an unfavourable outcome compared to new cases (aOR 0.54, 95%CI 0.31–0.93; P = 0.027). Conclusion: This study identified substantial gaps in TB care, including low rates of bacteriological diagnosis and HIV testing, and high rates of loss to follow-up, highlighting the need to strengthen TB control efforts, including support for new cases.