Aim: to determine the factors affecting medication adherence in diabetes mellitus patients. Methods: A prospective cross-sectional study was conducted in the Darbhanga Medical College and Hospital, Laheriasarai, Darbhanga,Bihar,India. for 12 months. All diabetes patients (both Type 1 and type 2) havingage more than 18 years and who were on diabetes medication were included. Total 200 patients were included in this study. A detailed questionnaire consisting of 25 questions whichincluded demographic details and the questions on the reasons for the treatment interruption were given to all thepatients visiting to study center. Results: Mean age, weight, height and BMI of study cohort was 48.55±11.12 years, 66.87±12.28kgs, 163.69±9.11cm and 26.15±4.12kg/m2 respectively. Majority of the patients were males 136 (68%). Of the 200 patients, majority were T2DM patients 196 (98%) followed by T1DM 4 (2%). Only 30 (15%) patients had family history of diabetes. Majority of the patients were illiterate 50 (25%) followed by 40 (20%)patients who were graduate. Majority of the patients weremarried 194 (97%), were businessman 50 (25%) andhad monthly income between 5001 to15000 rupees 40(20%). Majority of the patients were on oral antidiabetic medications 150 (75%) followed by Ayurvedic plus OralAntidiabetic medication 40 (20%). Only, 10(5%) patients were on insulins. In present study majority of the patients were off the treatment since 1-5 months 160(80%) followed by 20(10%) patients who were off the treatment since 6-10 months. Most common response for the treatment interruption was long life medication period (73%) followed by the fact that majority were not aware of the consequences of missing the doses (70%), 66% due to the side effect of the medication and 60% had financial problem. Conclusions: Large number of diabetes patients had poor adherence. There are many modifiable factors which can be improved on individual basis to improve the glycemic outcomes.