Introduction: In India TB report 2014 it was stated that, out of the estimated global annual incidence of 8.6 million TB cases, 2.3 million were estimated to have occurred in India till 2012. As per WHO, Tuberculosis prevalence per lakh population has reduced from 465 in year 1990 to 230 in 2012. Defaulting from treatment has been one of the major obstacles to treatment management and an important challenge for TB control. To ensure treatment adherence, Directly Observed Treatment - Short Course (DOTS) is a main strategy. It becomes imperative to understand the determinants of default under DOTS so that necessary actions can be taken up to prevent defaults under the program. Hence, the present study was undertaken to study the determinants of default under DOTS. Material and methods: Case control study was carried out in __ampersandsignldquo;Bhavani Nagar__ampersandsignrdquo; urban slum area of Hyderabad in old city and study subject were selected. Study duration was from 1st January 2011 to 31 December 2012 and data was collected from June 2013 to July 2013 by interviewing study subjects. The data collected was entered and analyzed using epi_info 6.04d. The study has been conducted after being approval from Institutional Ethical Committee. Results and conclusion: The odds of getting default were 2.4 times more when the study subjects belongs to OBC caste but was not found statistically significant. The risk of getting defaulter was 3.2 times more in study subjects studied less than higher secondary when compared with study subjects studied more than equal to higher secondary but was not found statistically significant. Major reason for defaulting was disappreance of the symptoms i.e. 33.3%, followed by intolerance of drugs(26.1%). It was found that having nuclear family is one of the determinant for defaulting. It was also seen that old cases of TB were associated with defaulting this may be due to the drugs intolerance or due to the disappearance of symptoms or their adherence to treatment requires more counseling. Defaulting was also found significantly associated with DOTS provider who were from the health department.