Introduction: Epilepsy is one of the recognized Central nervous System (CNS) complications in HIV infected patients. However, so far there were unknown researches conducted regarding the prevalence of epilepsy among HIV infected adult patients in Ethiopia in general and in the study area in particular. Objectives: The study was conducted to determine the prevalence of epilepsy among HIV infected adult patients who were on Anti-retroviral treatment (ART) in Adama Hospital Medical College, 2017. Methodology: Hospital based cross-sectional study was conducted using quantitative data collection method. A total of 748 HIV infected adult patients on Anti-retroviral treatment were recruited. Face to face interview was conducted using pretested structured questionnaire to collect the data. The imaging and laboratory results were extracted from Anti-retroviral treatment Logbook using checklist. The collected data was entered using Epi Info version 7 and exported to SPSS version 21 for analysis. Results: The prevalence of Epilepsy among HIV infected adults patients on ART was 15.4% (95% CI: 12.7, 17.9). The most common opportunistic infections were Cryptococcal meningitis and Toxoplasmosis. Conclusion and Recommendations: The prevalence of Epilepsy among HIV infected adult patients taking ART is high. The health care providers should take in to account for the need of testing for HIV in adults while diagnosing Epilepsy.