Background Advanced sinonasal malignancies invading the skull base/orbit traditionally require open craniofacial resection (CFR) with high morbidity. Purely endoscopic endonasal surgery (EES)—established for early disease—remains debated for T3/T4 cases due to en bloc resection challenges. This study assesses EES oncological safety and outcomes in a 2019–2023 cohort. Objective Evaluate feasibility, margins, survival, and morbidity of endoscopic resection for T3/T4 sinonasal malignancies. Methods Retrospective review of 47 patients with T3/T4 tumors: squamous cell carcinoma (38.3%), adenocarcinoma (23.4%), olfactory neuroblastoma (17.0%), adenoid cystic carcinoma (10.6%), sinonasal undifferentiated carcinoma (6.4%), melanoma (4.7%). All had primary EES with frozen-section margins. Median 24-month follow-up for OS/DFS (Kaplan-Meier), compared to open benchmarks. Results R0 margins in 83% (39/47). 2-year OS 74%, DFS 62%—comparable to CFR. Orbit preserved in 89% with medial involvement. Mean stay: 3.8 days. Complications: CSF leak (4.2%), epistaxis (2.1%); no mortality. Discussion EES enables precise modular resection with clear margins, equivalent survival, and less trauma—facilitating prompt adjuvant IMRT. Limits: extensive lateral/brain invasion. Conclusion EES offers safe, effective T3/T4 resection with oncologic parity to open surgery, lower morbidity, and better quality of life, supporting its multidisciplinary role.