Abstract Background Fast initiation of ART has been associated with higher rates of retention in HIV care and viral suppression at 48 weeks and with lower mortality rates. However, scarce evidence exists in our setting, where diagnosis and treatment are carried out in different contexts. Methods An observational retrospective study evaluating efficacy and safety of ART prescribed at the first specialist appointment, without baseline laboratory data, in a tertiary hospital in downtown Madrid. Individuals with a new diagnosis of HIV infection who initiated treatment at their first appointment with an infectious diseases specialist before receiving baseline laboratory results were included, irrespective of the ART regimen chosen. Results One hundred and eight participants were included. The majority (99.1%) were MSM who had acquired infection during sexual intercourse. The efficacy of ART, without baseline laboratory results at the time of initiation, was 85.2% (92/108) in the ITT analysis and 91.7% (99/108) in the treatment-related discontinuation equals failure analysis. All but nine patients presented an undetectable viral load (<50 copies/mL) at 48 weeks from starting ART. No serious adverse effects associated with the strategy were observed. In total, 101 participants continued care at 48 weeks with retention in HIV care rate of 93.5% (101/108). Conclusions Initiating ART at the first available opportunity without baseline laboratory data does not reduce efficacy or safety of ART and achieves rapid virological control with high rates of retention in HIV care.