The anteromedial region of the knee is little explored in the literature and may play an important role in anteromedial rotatory instability. The purpose of this study is to describe a ligamentous structure in the anteromedial region of the knee identified in a series of anatomical dissections of cadaveric specimens. Twenty-one cadaveric knees were dissected to study the medial compartment. Exclusion criteria were signs of trauma, previous surgery, signs of osteoarthritis, and poor preservation state. The main structures of this region were identified during medial dissection. After releasing the superficial medial collateral ligament of the tibia, the anterior oblique ligament (AOL) was isolated. The morphology of the structure and its relationship with known anatomical parameters were determined. For the statistical analysis, the means and standard deviations were calculated for continuous variables. A 95% confidence interval was defined as significant. Student's t-tests were used for continuous variables. After dissection, a distinct ligamentous structure (AOL) was found in the medial region of the knee. This structure was found in 100% of the cases, was located extracapsularly and originated in the anterior aspect of the medial epicondyle, running obliquely toward the tibia. When crossing the joint, the ligament presented a fan-shaped opening, exhibiting a larger area at the tibial insertion. The AOL had a mean thickness of 6.83 ± 1.51 mm at its femoral origin and 13.39 ± 2.64 at its tibial insertion. It had a significantly (p = 0.0001) longer mean length with the knee at 90° of flexion (35.27 ± 6.59 mm) than with the knee in total extension (27.89 ± 5.46 mm), indicating that the ligament is tensioned in flexion. A new structure was identified in the anteromedial compartment of the knee with a ligamentous appearance. Further studies are necessary to identify its importance on knee stability. This study demonstrates the anatomy of a new medial structure of the knee. As a result, there will be a better understanding of the stability of the knee.