We investigated the experiences of Brazilian gay men with HIV, focusing on the moment of diagnosis and its potential biopsychosocial impacts. This clinical-qualitative study involved 15 participants interviewed online and synchronously by a clinical psychologist in 2021. Thematic analysis was employed to analyze the data. Interpretations were grounded in Minority Stress Theory. Four thematic axes emerged, including "Diagnostic Revelation", "Social and Internalized Stigma", "Biopsychosocial Effects of Living with HIV", and "Gratitude for Treatment Advances and the Brazilian Health System". The diagnosis was often experienced as traumatic, exacerbated by the absence of empathy and emotional support from healthcare providers. Participants commonly reported guilt, fear upon learning of their HIV status, social isolation, loneliness, lack of social support, and damage to affective-sexual relationships. Many also noted a decline in mental health, even those without HIV-related medical complications. Despite over 40 years since the HIV epidemic began, the prevalence of homophobia and serophobia among gay men remains widespread, including within the multidisciplinary teams of specialized services. This indicates that the stigma associated with homosexuality and HIV persists, despite significant biomedical progress in the diagnosis and treatment of the infection, particularly in Brazil.