BACKGROUND Fibrous connections and fibrofatty tissue between the layers of the medial retinaculum have prevented accurate definition of the true anatomy of the medial patellofemoral ligament. This has led to confusion about the origin, form, course, and insertion of this structure. OBJECTIVE The medial patellofemoral ligament is a discrete structure that can be approached, isolated, and definitively described. METHODS Descriptive laboratory study. METHODS Fifty fresh or fresh-frozen human knee specimens were carefully dissected to determine the precise anatomy of the medial patellofemoral ligament. RESULTS Present in all specimens, the medial patellofemoral ligament was found to have 2 origins: (1) a transverse 10.6-mm origin from the bony groove between the medial epicondyle and the adductor tubercle, and (2) an oblique decussation originating from the proximal 30 mm of the leading edge of the superficial medial collateral ligament. The 2 origins combined and inseparably joined the vastus medialis obliquus tendon and inserted securely into the ventral edge of the bony patella over a span of 28.2 + or - 5.6 mm adjacent to the articular surface of the patella. The length from the femoral origin to the patella was 59.8 + or - 4.8 mm. The key to the dissection was finding the fine capsular vessels from the descending genicular artery that is between layers I and II of the medial retinacular structures. CONCLUSIONS The medial patellofemoral ligament is a constant structure in ladouble daggeryer II, with a complex anatomy that can be defined by careful dissection using the capsular branches of the descending genicular artery as a guide. CONCLUSIONS This study provides essential new information that could help surgeons safely locate the medial patellofemoral ligament and repair or reconstruct it anatomically.