BACKGROUND Good adherence to highly active antiretroviral therapy (HAART) is required for viral suppression and prevention of drug resistance. Patients' adherence to HAART has not been determined since the commencement of HAART at the University of Ilorin Teaching Hospital (UITH), Ilorin, Nigeria, over 5 years ago. OBJECTIVE To determine the adherence level of people living with HIV/AIDS (PLWHA) to HAART and identify associated factors. METHODS A semistructured questionnaire was administered to PLWHA, who were accessing treatment. Sociodemographic, lifestyle, HIV medical, and drug history were obtained from them. Adherence was self-reported. Good adherence was taking of 95% of the prescribed doses of HAART over the preceding 30 days before consultation. RESULTS Study participants were 253; majority, 58.5%, were females. About 70.8% of them had good adherence. Older age and male sex correlated better with adherence. CONCLUSIONS People living with HIV/AIDS were quite adherent to HAART. Male sex and older age were positive predictors of adherence. Adherence among the young age and females needs strengthening.