Introduction Standard treatment duration for drug-susceptible tuberculosis (TB) treatment is 6 months. Treatment duration is often extended-and for various different reasons. The aim of this study was to determine the prevalence and to assess risk factors associated with extended TB treatment. Methods A cross-sectional study was conducted. Data including demographic, clinical, radiological and microbiological information from the Netherlands TB Register (NTR) of 90 patients with smear and culture positive pulmonary TB of the region Haaglanden, The Netherlands, was eligible for analysis. Results Treatment was extended to >= 200 days by 46 (51%) patients. Extended TB treatment was associated with a higher frequency of symptoms, presumed to be due to adverse drug reactions (ADR; OR 2.39 95% CI: 1.01-5.69), drug-induced liver injury (DILI) (OR: 13.51; 95% CI: 1.66-109.82) and longer than 2 month smear and culture conversion rate (OR: 11.00; 95% CI: 1.24-97.96 and OR: 8.56; 95% CI: 1.53-47.96). In the multivariable logistic analysis, development of DILI emerged as the single statistically strong risk factor necessitating extension of TB treatment. Conclusion This finding will need further confirmation in a prospective study, exploring the possible mutual role of pharmacokinetic and pharmacogenetic determinants of DILI among TB patients.