Objective: Biportal endoscopic spine surgery (BESS) has emerged as a minimally invasive alternative for lumbar decompression, offering improved visualization with reduced tissue disruption. Therefore, this study aims to identify key anatomical considerations, particularly interlaminar-disc mismatch and the “banana-shaped” curvature of the lamina, and to examine their impact on portal trajectory, alignment of the surgical corridor, and preservation of spinal structures. Methods: A retrospective, video-based analysis was conducted on 23 BESS lumbar decompression cases performed between January and March 2024. Surgical levels included L3–4 (n=3), L4–5 (n=17), and L5–S1 (n=3). Intraoperative anatomical landmarks were assessed independently by 2 spine surgeons. Interobserver agreement was evaluated using Cohen kappa, based on the identification of 3 landmarks per case in 23 cases, calculated with unweighted kappa. Visualization quality was scored on a 3-point scale. Cranial and caudal interlaminar-disc mismatches were measured and averaged. Results: Interlaminar-disc mismatch was identified in 93% of cases, with cranial and caudal mismatches ranging from 5.5±1.02 mm to 8±1.2 mm. Laminar curvature was consistently observed at L4–5 and L5–S1, which required a medial-caudal portal. In addition, the superior articular process (SAP) served as a reliable fluoroscopic and endoscopic landmark, facilitating safe access to the intervertebral disc. A limited medial facetectomy provided adequate operating space. The findings also demonstrated high interobserver reliability for anatomical identification (κ=0.84), and the use of layer-specific flavectomy preserved the inner layer of the ligamentum flavum. Conclusion Successful BESS requires integrating detailed anatomical understanding with intraoperative adaptability. Recognizing interlaminar-disc mismatch, laminar curvature, and SAP orientation enables optimal portal placement and targeted decompression. These principles are essential for achieving reproducible and safe outcomes in BESS.