Treating tuberculosis (TB) remains a public health challenge in many developing countries. Treatment success rate in Malaysia is on declining pattern from 78% in 2000 to 48% in 2006. This study will determine factors associated with unsuccessful treatment among pulmonary TB patients. A retrospective cohort study was conducted on notified and treated pulmonary TB cases in Kota Bharu district Kelantan between January 2006 and December 2007. To identify the associated factors, univariate comparison and multiple logistic regressions were performed. Among the 765 patients identified, 472 (61.7%) cases fulfilled the criteria and were analyzed. There were 316 males and 156 females and their mean (SD) age was 45 (17.9) years. In univariable analysis, age, gender, educational level, employment status, family incomes as well as co-existence of extra-pulmonary TB, smoking, co-morbid disease (diabetes mellitus), HIV status, sputum cultures, chest X-ray findings and duration of delay for diagnosis were all found to have significant relationship with unsuccessful pulmonary TB treatment outcome. After adjusted for the confounders, the significant predictors for unsuccessful tuberculosis treatment were age (Adj. OR 1.09; 95% CI: 1.03-1.15), HIV positive (Adj. OR 23.04; 95% CI: 3.01-176.22) and advanced chest X-ray findings (Adj. OR 6.51; 95% CI: 1.50-28.23). A large proportion of unsuccessfully treated cases could be identified at entry by screening for age, chest X-rays and HIV status and specially targeted measures could be taken. The use of directly observed treatment short-course (DOTS) should be given more focus and priority among this high risk group of patients.