Because persons who identify across the transgender spectrum (PATS) are a key population in human immunodeficiency virus (HIV) yet are underreported in HIV and cardiovascular research, we aimed to characterize this population within the REPRIEVE global clinical trial (n = 7770). Acceptance of gathering gender identity was high (96%). Participation by PATS was 1.7% overall, 2.4% among natal males, 0.3% among natal females, and varied across geographic regions (from 0% in sub-Saharan Africa to 2.3% in High Income Region). Thirty percent of natal male PATS identified other than transgender. Some characteristics differed by gender. Most notably, 38% of natal male PATS receiving gender-affirming treatment had waist circumference >102 cm (compared with ≤25% in other groups). Given that PATS is a key population, HIV research should routinely report trial participation and outcomes by gender in addition to natal sex, to provide the results needed to optimize medical care to PATS.