Introduction: In the EU/EEA, men who have sex with men (MSM) is a priority group for the prevention and control of HIV-1 infection. In Portugal, the 2023 HIV incidence rate was 8.2 per 100,000 inhabitants, with 876 new infections, 41.7% in MSM. We aim to characterize HIV-1 transmission clusters (TC) and transmitted drug resistance (TDR) and its sociodemographic, behavioral, clinical, and viral genomic determina...