Background: Number of HIV cases continues to rise among young (18-30 years) gay, bisexual, and other men who have sex with men (MSM) and transgender women (TGW) in Latin America. ImPrEP was a PrEP implementation study conducted in Brazil, Peru, and Mexico. We describe characteristics of HIV seroconversions in ImPrEP by country. Methods: Eligible MSM and TGW (HIV-negative, =18 years, reporting 1+ risk criteria) were screened and enrolled on the same day and received a 30-day oral TDF/FTC PrEP supply. Follow-up visits were scheduled 4 weeks post-enrolment and quarterly thereafter. HIV rapid testing was performed at all visits. We compared demographic (at enrollment) and behaviour (last visit prior to seroconversion) characteristics using chi-square or exact tests for the contigency tables and Kruskal Wallis tests for medians. Results: From February 2018-June 2021, 9509 MSM/TGW were enrolled (Brazil: 3928 [41.3%]; Mexico: 3288 [24.6%]; Peru: 2293 [24.1%]); 104 were diagnosed with HIV during 12,185.25 person-years of follow-up. Overall, 76.0% were young, 82.7% non-white, and 71.3% completed secondary education or more. The median number of partners was 5 (IQR:2-15); 70.2%, 92.2% and 85.6% reported receptive condomless anal sex, inconsistent condom use and incomplete PrEP adherence, respectively. The median number of days between the first PrEP dispensation and HIV diagnosis was 360 days, higher in Brazil (541 days) and lower in Mexico (242 days). The median HIV viral load after diagnosis was 12,257 copies/mL, lower in Mexico (3680 copies/mL) and higher in Peru (50100 copies/mL). Viral mutations detected were: 1 (1.8%) K70 and 6 (10.5%) M184V/I (Table). Conclusions: We observed poor adherence among MSM and TGW who seroconverted during the ImPrEP study. Long-acting PrEP may be an appropriate strategy to overcome adherence barriers observed among young MSM and TGW in Latin America.