Introduction: Rapid antiretroviral therapy (ART) initiation is recommended for all people living with human immunodeficiency virus (HIV). Time to ART initiation in individual patients depends on several factors. The study objectives were to investigate the time to ART initiation in HIV-positive patients with opportunistic infections/AIDS-defining illnesses (OIs/ADI), and associated factors. Material and methods: A prospective cohort study was performed among ART-na & iuml;ve HIV patients with OIs/ADI. Time to ART initiation was defined as the time from being diagnosed with OIs/ADI to Results: A total of 253 patients were included. The three most common OIs were tuberculosis (36.8%), Pneumocystis jirovecii pneumonia (26.1%), and candidiasis (19.0%). 39.9% of patients learned about their HIV-serostatus after OIs/ADI diagnosis. The median time from OIs/ADI diagnosis to ART initiation was 38 days (IQR, 23-71). From Cox regression model, the factor independently associated with a shorter waiting time to ART initiation was continuous engagement in HIV care (aHR = 2.42; 95% CI: 1.70-3.45%). On the other hand, the factors associated with a longer time to ART initiation were tuberculosis co-infection (aHR = 0.52; 95% CI: 0.36-0.75%), HIV diagnosis after OIs/ADI (aHR = 0.42; 95% CI: 0.30-0.57%), viral hepatitis B/C co-infection (aHR = 0.59; 95% CI: 0.39-0.89%), seeking care in general hospital and community hospital (aHR = 0.67; 95% CI: 0.49-0.93%, and aHR = 0.62; 95% CI: 0.44-0.86%, respectively), having more than one hospital admission in the past six months (aHR = 0.60; 95% CI: 0.44-0.81%), and history of missed appointments (aHR = 0.62; 95% CI: 0.42-0.91%). Conclusions: To achieve maximal benefits of ART, strategies to improve HIV awareness, continuous care engagement, and timely ART initiation are required.