The most common cause of anterior cruciate ligament (ACL) reconstruction failure is known to be malposition of the femoral tunnel. During revision, creating a femoral tunnel in an accurate anatomic footprint is key. It is difficult to observe the femoral footprint from the anterolateral or anteromedial portal, because it is obscured by the ACL graft remnant or the ridge of the medial wall of the lateral femoral condyle, especially in revision ACL reconstruction. In revision ACL reconstruction, viewing through a trans-septal (TS) portal allows the entire femoral footprint to be identified directly. Additionally, the relationship between the previous femoral tunnel and the new femoral tunnel can be easily checked, and the surgeon can confirm any sign of overlapping between two tunnels. After tunneling, any inner surface fracture can be identified through arthroscopy. We used a TS portal as a viewing portal while making a new anatomic femoral tunnel via the outside-in technique during revision ACL reconstruction. First, the surgeon made a posteromedial (PM) and a posterolateral (PL) portal. A round trocar was inserted through the PL portal. While pushing the trocar, the surgeon made a hole on the posterior septum via arthroscopic shaver. Shaving was done via the central working portal while the surgeon viewed it from the PM portal. The septum was removed via arthroscopic shaver through the PL portal. After making the TS portal, the surgeon advanced the arthroscope through the PM portal and the posterior septum. Through the TS portal, the surgeon obtained a direct view of the femoral footprint of the ACL and the previous femoral tunnel. If the surgeon saw, via the TS portal, previous tunnel malposition distant from the anatomic footprint, the surgeon made a new anatomic tunnel via the outside-in technique. Since 2017, 30 patients in our center have undergone revision ACL reconstruction involving the use of the TS portal. Among them, 11 patients were followed up for 24 months or longer. The patient-reported outcomes (obtained via the Lyshom Knee Scoring Scale, the International Knee Documentation Committee Subjective Knee Form, and the Tegner Activity Scale) were improved at 24 months after surgery. All patients had laxity within 3 mm (International Knee Documentation Committee grade A). Postoperative three-dimensional CT was obtained in all patients and showed that all newly made femoral tunnels were safely in the anatomic footprint and had no overlap with the previous tunnels.