Background: Same-day HIV testing and antiretroviral therapy (ART) initiation is being widely implemented. However, the optimal timing of ART among patients with tuberculosis (TB) symptoms is unknown. We hypothesized that same-day treatment (TB treatment for those diagnosed with TB; ART for those not diagnosed with TB) would be superior to standard care in this population. Methods and findings: We conducted an open-label trial among adults with TB symptoms at initial HIV diagnosis at GHESKIO in Haiti; participants were recruited and randomized on the same day. Participants were randomized in a 1:1 ratio to same-day treatment (same-day TB testing with same-day TB treatment if TB diagnosed; same-day ART if TB not diagnosed) versus standard care (initiating TB treatment within 7 days and delaying ART to day 7 if TB not diagnosed). In both groups, ART was initiated 2 weeks after TB treatment. The primary outcome was retention in care with 48-week HIV-1 RNA <200 copies/mL, with intention to treat (ITT) analysis. From November 6, 2017 to January 16, 2020, 500 participants were randomized (250/group); the final study visit occurred on March 1, 2021. Baseline TB was diagnosed in 40 (16.0%) in the standard and 48 (19.2%) in the same-day group; all initiated TB treatment. In the standard group, 245 (98.0%) initiated ART at median of 9 days; 6 (2.4%) died, 15 (6.0%) missed the 48-week visit, and 229 (91.6%) attended the 48-week visit. Among all who were randomized, 220 (88.0%) received 48-week HIV-1 RNA testing; 168 had <200 copies/mL (among randomized: 67.2%; among tested: 76.4%). In the same-day group, 249 (99.6%) initiated ART at median of 0 days; 9 (3.6%) died, 23 (9.2%) missed the 48-week visit, and 218 (87.2%) attended the 48-week visit. Among all who were randomized, 211 (84.4%) received 48-week HIV-1 RNA; 152 had <200 copies/mL (among randomized: 60.8%; among tested: 72.0%). There was no difference between groups in the primary outcome (60.8% versus 67.2%; risk difference: −0.06; 95% CI [−0.15, 0.02]; p = 0.14). Two new grade 3 or 4 events were reported per group; none were judged to be related to the intervention. The main limitation of this study is that it was conducted at a single urban clinic, and the generalizability to other settings is uncertain. Conclusions: In patients with TB symptoms at HIV diagnosis, we found that same-day treatment was not associated with superior retention and viral suppression. In this study, a short delay in ART initiation did not appear to compromise outcomes. Trial registration: This study is registered with ClinicalTrials.govNCT03154320. In an open-label randomized trial from Haiti, Nancy Dorvil and colleagues investigate the effectiveness of same-day TB testing and treatment initiation in adults with TB symptoms at HIV diagnosis compared to standard care. Author summary: Why was this study done?: HIV treatment guidelines worldwide recommend that antiretroviral therapy (ART) be initiated immediately or as soon as possible after HIV diagnosis, to improve linkage to care and treatment uptake. A substantial proportion of patients present with symptoms of tuberculosis (TB) at HIV diagnosis. TB testing is ideally conducted prior to ART initiation in symptomatic patients. The optimal timing of ART initiation for this patient population is unknown. From the health center perspective, a short delay in ART initiation facilitates TB testing. However, this strategy may result in extra visits for patients, which may result in loss to follow-up (LTFU). What did the researchers do and find?: We conducted a randomized trial to assess the effectiveness of same-day TB testing and treatment initiation (TB medication if TB diagnosed; ART if TB not diagnosed) on the day of HIV diagnosis versus standard care, in adults with TB symptoms at HIV diagnosis in Haiti. We found near universal ART initiation in both the same-day treatment and the standard groups. Same-day treatment was not associated with higher rates of retention in care with viral suppression at 48 weeks after enrollment, compared to the standard group. This was the primary outcome of the study. What do these findings mean?: Our findings indicate that both strategies are effective. Same-day TB testing and treatment initiation may be preferred at sites with this capacity, but short delays in treatment initiation do not appear to compromise outcomes. An important caveat is that treatment was provided rapidly in the standard group, reflecting current standard practice. This study is limited by being conducted at a single, large, urban HIV clinic in Haiti. Further study will be necessary to determine if these findings are reproducible in other settings. [ABSTRACT FROM AUTHOR]