OBJECTIVES: To evaluate incidence, onset and severity of Adverse Drug Reaction profile of first line anti-tubercular drugs. To evaluate causality of ADRs and determine association of ADRs with demography & smoking METHODS: This prospective study included 60 cases of newly diagnosed patients on first line anti-tubercular therapy. Patients of either sex aged 18 - 70 years were included. Clinical, biochemical and physical examination was done at start, 2^nd month and after treatment. ADR severity and causality were assessed using Hartwig Severity assessment scale and Narango Algorithm respectively. The statistical analysis was done using ANOVA test. RESULTS: Patients older than 40 years had higher proportion of ADRs (60% versus 40%). The proportion of ADRs was more common in women (55% versus 45%) than men.The incidence of organ systems most affected by ADRs were the gastrointestinal tract [GIT] (50%) followed by skin (10%), hepatobiliary system (6%), hematologic system (1.5%), ototoxicity (2.5%) and renal system (4%).The earliest onset of ADRs was GIT (15 days) followed by skin, hepatobiliary system, renal system ,hematologic system and ototoxicity .The onset of ADR was earlier in older than 40 years age group by a mean of 5 days. All ADRs were mild in severity except (10 % of GIT) ADRs which were moderate but no severe reactions.On evaluation of causality of all ADRs reported, majority (90%) of them were in ‘probable’ category. The frequency of smokers was 20 % reporting a higher incidence of ADR (58% versus 42%) than non-smokers. CONCLUSIONS: Incidence of ADRs due to anti-TB therapy was 56.4% with majority of GI symptoms highlighting the importance of developing strategies to ameliorate ADRs both to improve the quality of patient care and to control TB safely.Age, gender and smoking are independent risk factors which significantly affect the incidence, onset and severity of drug induced ADRs