OBJECTIVE To assess treatment outcomes and determinants of outcome among tuberculosis patients. METHODS A longitudinal study design involving a cohort of sputum smear-positive pulmonary tuberculosis patients at initiation of therapy, who were followed up to the end of treatment at eighth month. METHODS Tuberculosis treatment centers in Ibadan, Nigeria. RESULTS A total of 1,254 patients were followed up with a mean age of 35.0+/-3.3 years. The percentages of patients with treatment outcomes assessed in the study were as follows: cure (76.6%), failure (8.1%), default (6.6%), transferred out (4.8%), and death (1.9%). The cure rate varied significantly between treatment centers from 40 to 94.4% (P<0.05). The treatment centers located within the specialist health centers at Jericho and the University College Hospital had 50 and 75% cure rates, respectively.The mean age of cured patients was 31.2+/3.1 years which was significantly lower than the mean age of those with poor treatment outcomes (36.7+/3.5 years; P<0.05). Males had a higher risk of a poor treatment outcome (RR=1.8; 95% CI: 1.02-1.94) than females. Also, patients with a poor knowledge of tuberculosis had a higher risk of having a poor treatment outcome (RR=1.35; 95% CI: 1.25-1.62) compared to those with knowledge. CONCLUSIONS Variations in health center treatment outcomes and poor knowledge of tuberculosis among patients suggest that poor program implementation quality may be a major modifiable determinant of treatment outcomes in our environment.