This study aims to evaluate the prevalence of previously undiagnosed HIV infection in the hospital setting (across various medical or surgical departments) among individuals exhibiting at least one HIV indicator condition (HIV-IC) and/or engaging in risky behaviors. This is a cross-sectional, single-center study with additional procedures. Data collection will involve clinical and laboratory data from individuals with at least one HIV-IC and/or behavioral risk factor for HIV infection admitted to the San Raffaele Hospital in Milan for any reason. The overall study duration is 24 months, with recruitment lasting 20 months. Individuals will be actively recruited from various medical or surgical units of the hospital. After obtaining informed consent, clinical and laboratory information related to the study will be collected, along with specific blood samples. The presence of at least one HIV-IC will be determined using available clinical, radiological, and laboratory parameters during hospitalization. Following informed consent, hospitalized individuals will complete a paper questionnaire, aimed at identifying behavioral risk factors for HIV infection. If at least one HIV-IC or behavioral risk factor is present, the person will be eligible for inclusion in the clinical study, and a rapid capillary HIV test will be conducted bedside. In case of a positive rapid capillary HIV test result, antigen/antibody testing and Western Blot for HIV confirmation will be performed on venous blood samples on the same day.