Lumbar foraminal stenosis (LFS) is a fairly common degenerative condition of the spine that can often occur in the L5–S1 segment. Traditional surgical approaches for LFS can be categorized into microscopic foraminotomy via the Wiltse approach and interbody fusion. Microscopic foraminotomy via the Wiltse approach was previously considered the gold standard for treating LFS. However, with advancements in endoscopic equipment and techniques, fully endoscopic foraminotomy through various approaches is now widely performed for the treatment of LFS. Among these approaches, endoscopic foraminotomy via the transforaminal approach offers many advantages, but difficulties may be encountered when there are anatomical barriers, which are often present in the L5–S1 segment. This study aimed to explore the overall clinical outcomes and complications of transforaminal endoscopic lumbar foraminotomy, as well as the challenges specific to the L5–S1 segment and techniques to overcome them.