Background: Adherence to treatment has been identified as a major predictor of survival in persons living with HIV/AIDS (PLWHA), and poor medication adherence has been identified as an important factor in treatment failure and development of drug resistance in patients on highly active antiretroviral therapy (HAART). Aim: This study was conducted to determine the prevalence and factors associated with treatment adherence among patients on HAART in Specialist Hospital, Sokoto, Nigeria. Materials and Methods: A cross-sectional study was conducted among 173 patients (selected by systematic sampling technique) attending the ART clinic of Specialist Hospital, Sokoto, Nigeria. A structured interviewer-administered questionnaire was used to collect data on the research variables. Data were analyzed using IBM SPSS version 23 statistical computer software package. Results: Most, 144 (83.2%) of the 173 respondents attained at least 95% adherence to the prescribed HAART regimen. The main reasons cited for missing their ART medication were being away from home (33.3%), being too busy (24.2%) and missing clinic appointments (24.2%). Whereas, adherence to treatment was associated with self-perception of health status as excellent and very good since commencing ART, it was not associated with any of the respondents’ socio-demographic variables. Conclusion: This study showed optimal adherence by majority of patients on HAART at Specialist Hospital, Sokoto, Nigeria, with adherence being associated with patients’ perception of their health status since commencing ART. These findings underscore the need for ART care providers to sustain adherence counseling, make treatment schedules patient-friendly, and consistently assess patients’ response to treatment from their own perspectives.