Background:For the successful treatment of human immunodeficiency virus (HIV), it is important that drugs should be taken regularly. Non-adherence not only increases chances of failure of treatment but also leads to the development of resistance to drugs and hence more focus has been given to adherence in the treatment protocol of HIV.Objectives:To determine the level of adherence, its determinants, and to ascertain reasons for non-adherence of antiretroviral therapy (ART) in patients with HIV/acquired immunodeficiency syndrome (AIDS).Methods:A cross-sectional study conducted at an adult ART clinic over a period of one year. The sample size was 320. A systematic random sampling technique was used. Semi-structured Adult AIDS Clinical Trials Group questionnaire was used. Beck Depression Inventory (BDI-II) for current depression and self-report of four days recall method and multi-method approach were used for adherence measurement.Results:The mean age of respondents was 37.26 ± 8.3 years. About 60.3% were males, 34.1% females, and 5.6% were transgenders (TGs). High adherence was found in 87.2% by self-report and 72.5% by multi-method approach. History of opportunistic infection and depression were found to be the best predictors of adherence. Reasons for short term non-adherence were found to be simply forgot to take medications, being away from home, busy with other things, and ran out of pills. Reasons for long-term non-adherence were financial difficulty, side-effects, and shift to alternate therapy.Conclusions:Significant non-adherence to ART necessitates addressing adherence issues in pre-ART counseling, the involvement of family and social support.