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Background: Early diagnosis of undetected HIV infection is essential for controlling transmission and improving patient outcomes. Emergency departments (EDs) are critical access points for identifying hidden cases. Since 2021, the VIHGILA project, implemented in 25 hospitals in Catalonia (Spain), has aimed to proactively diagnose HIV infection across six clinical scenarios: suspected sexually transmitted infection (STI), chemsex, post-exposure prophylaxis (PEP) request, mononucleosis-like syndrome, community-acquired pneumonia (ages 18–65), and herpes zoster (ages 18–65), as recommended by a national Consensus Document (CD). Methods: A prospective, observational study was conducted across 25 Catalan EDs. Between 2021 and 2025, 25 EDs implemented an opt-in strategy to test every patient with targeted conditions on top of other classical reasons for HIV testing. Post-implementation HIV screening new diagnoses in EDs were described. HIV seroprevalence was calculated overall and per clinical scenario. A sub-analysis was performed on patients diagnosed at Hospital de Sant Pau (HSCSP). Results: From July 2021 to August 2025, 47,198 HIV tests were performed, of which 21,317 (45%) were conducted under CD-defined indications. A total of 427 new HIV diagnoses were made (overall prevalence: 0.90%), with 216 (51%) occurring in CD-identified risk scenarios: STI: 0.8% (47/5,780), Chemsex: 4.6% (10/216), PEP: 0.4% (14/4,171), Mononucleosis-like syndrome: 1.6% (26/1,638), Pneumonia: 1.2% (89/7,798), Herpes zoster: 1.4% (15/1,071). At HSCSP, 26 patients were diagnosed from 2,684 HIV tests (1.0%). Mean age 36 years (22–59), 90% male. 11 cases met CD criteria. Baseline CD4 count was 300 cells/mm³, 12 patients presenting CD4 <100 cells/mm³. Viral load was 1.7 million copies/mL. 15 patients (58%) were linked to HIV care within one month (mean follow-up: 12 months), others were referred to external centers. 3 patients (11%) were lost to follow-up. All patients initiated ART with Biktarvy; follow-up CD4 count averaged 588 cells/mm³, and all but two achieved an undetectable viral load. Conclusions The VIHGILA project is an effective and feasible strategy for identifying undiagnosed HIV infection in EDs. HIV incidence approaches 1%, significantly exceeding the thresholds that support the implementation of screening programs.Among the cohort from HSCSP, Half of the diagnosed patients were Spanish nationals. Rapid linkage to care and early initiation of ART, primarily with Biktarvy, led to favorable immunovirological outcomes.