Introduction - Transgender people are highly vulnerable to HIV infection and other STIs due to behavioral, economic, and social factors. The aim of this study is to describe HIV diagnoses in this population. Materials and Methods - The data were obtained from mandatory reporting of HIV infection. The analysis focused on HIV diagnoses among transgender individuals between 2012 and 2020. Two categories were identified: seroconversions (individuals unaware of their HIV status prior to diagnosis) and first-time diagnoses in France of individuals previously diagnosed in another country. Results - From 2012 to 2020, 253 transgender individuals discovering their HIV-positive status were reported, representing 0.7% of all new diagnoses during this period. After adjusting for underreporting and missing data, this number is estimated at 418 (95% CI: [367–469]). Most of these individuals were transgender women (87%), with a median age of 31 years (38.5 for men). Transgender women were more likely to have been born abroad (83%, mainly in South America) than transgender men (52%). The likely mode of transmission was primarily sexual (98%). The most common reason for serology testing was recent exposure to HIV (33%), and 15% of diagnoses were made following a positive rapid diagnostic test (RDT). One in five transgender individuals was diagnosed at an advanced stage of infection (AIDS or <200 CD4), and 37% of transgender individuals were co-infected with another STI. Between 2012 and 2020, 115 transgender individuals who were aware of their HIV status and diagnosed in France in the year of their arrival in the country were reported, representing 6% of those diagnosed under these conditions. These diagnoses concerned almost exclusively women (99%). After adjustment, their number is estimated at 169 (95% CI: [137–201]) individuals. Discussion and Conclusion - The vast majority of transgender individuals discovering their HIV-positive status were born abroad and infected through sexual transmission. They are frequently co-infected with a bacterial STI, highlighting their high level of sexual exposure and underscoring the need to strengthen diversified prevention efforts in this population, particularly through PrEP. Diagnosis at an advanced stage of infection is more common among trans people born abroad who are diagnosed several years after their arrival, underscoring the need to continue encouraging testing even after migration. Like the discovery of HIV-positive status, initial diagnoses in France of individuals already diagnosed in another country represent a significant challenge in terms of establishing medical care, whether it involves initiating or continuing antiretroviral treatment.