Background: Same day or rapid ART initiation was suitable for asymptomatic HIV stage. Studies have shown benefits in faster virological suppression and reduction of loss to follow up rate. Objective: To compare virological outcome at 24 and 72 weeks in adult HIV infection starting ART within two weeks as the rapid ART group, or more than two weeks as the standard care group. Materials and Methods: A retrospective cohort study was conducted at Chiangrai Prachanukroh Hospital, Chiangrai, Thailand. All new cases of patients diagnosed with HIV infection between October 1, 2012 and September 30, 2019 were included. The study included demographic data and virological outcome at 24 weeks and 72 weeks, status of loss to follow up or death. Results: One thousand seven new adult HIV cases were reviewed. Mean age was 34.03±11.27 years old. Male was predominant at 70.51%, mode of transmission was heterosexual at 87.49%. Median CD4 of cases was 268 cells/mm³. Of all the cases. 36.6% of cases were prescribed ART within 14 days with a median of eight days. NNRTI base regimen was given in 93.64% of the cases. Virological suppression less than 40 copies/mL at 24 weeks was 84.94% in rapid ART group compared with 82.92% in standard group. There was no statistical difference between the groups (p=0.747). Virological suppression less than 40 copies/mL at 72 weeks was 97.14% in rapid ART group compared with 93.84% in standard group, with no statistical difference (p=0.079). Retention to care was higher in rapid ART groups (p=0.012) and mortality rate was lower in rapid ART group (p=0.003). Loss to follow up rate was not different between the groups. Conclusion: There was no differences in virological outcome and loss to follow up between the rapid ART and standard groups, but there was better retention to care and lower mortality rate in the rapid ART group. Keywords: Adult; HIV; Rapid ART; Virological outcome; LTFU; Thailand