Considering the importance of nutritional health for people living with HIV, programs delivering nutritional support have been scaled up globally. Among various programs, the Food by Prescription (FBP) program has been implemented in Ethiopia since 2010. This study was undertaken to assess the level of adherence to the FBP program and identify the associated factors among HIV infected adults. Facility-based cross-sectional study design was conducted from May to June 2018 among 481 adult people living with HIV who have been enrolled in the program in 15 public health facilities. The study subjects were selected through a convenient sampling technique and data were collected using a structured interviewer-administered questionnaire. The data were entered and analyzed using Epi Info version 7 and Statistical Package for Social Science version 20 statistical software respectively. Bivariable and multivariable logistic regression were used. More than half 285(59.3) of the study subjects were found to be adherent to the FBP program. The amount of prescribed food, the duration of stay in nutrition program, the practice of sharing the supplement and experiencing of supplement stock out was found to be the most important predictors. The study revealed the level of adherence to the FBP program and identified some of the most important associated factors among adult people living with HIV. Strengthening the counseling component of the program, improving the supply management of the health facilities and linking people living with HIV to the economic strengthening activities should be considered to improve the adherence level of the program.