Background: High level of Antiretroviral Therapy adherence among HIV infected patients contributes to better treatments outcome and has additional importance in preventing the development of drug resistance. It also improves the quality of life and makes the patient live longer and healthier. The objective of the study was to determine level of adherence as well as factors influencing adherence to antiretroviral therapy among HIV infected patients in Nyamagana district, Mwanza, Tanzania.