Objective: Isoniazid (INH) is given to individuals with latent infection of tuberculosis in order to prevent progression to active disease. It is important to understand factors associated with non-adherence to prophylactic Isoniazid. This study aimed to identify correlates of adherence and utilization of Isoniazid in HIV positive patients and to explore the opinions of patients and health care providers. Methods: Participants eligible for the study were 403 randomly selected HIV positive individuals taking INH on follow up in Yekatit 12 hospital. Adherence was measured by self-report of INH tablets taken for past 3, 7 and 30 days. In depth interview was also conducted on recruited patients and health professionals. Results: Adherence to INH was 94% for last 7 days. INH related common side effects were reported by 142 participants (35.2%) and only 53 (13.2%) discontinued. The odds of adherence was 104, 7.7 and 34.8 [95% Confidence Interval (18.7, 582.6), (2.6, 22.9) and (4.4, 272.6)] times higher among those patients who did not have jaundice, skin rash and seizure compared to those who developed, respectively. Conclusion: The prevalence of adherence to INH in Yekatit 12 hospital was better than other local and African studies and the reasons for poor adherence was strongly associated with occurrence of jaundice, skin rash and seizure. Comprehensive care and support, sustainable drug supply and evaluation of side effects are recommended.