The anatomical and functional details of the cruciate ligaments of the knee were studied on 20 cadaver knees and 24 fresh knees. Each anterior cruciate ligament was found to consist of 2 parts: a distinct antero-medial band (AMB) and a main postero-lateral part. The exact geometry of the ligaments and their relationship to bony landmarks were recorded in detail. The state of the cruciate ligaments, i.e. tightness or looseness was recorded in the various positions of the knec as the basis for classification of the function of the various anatomical components. Selective cutting of the anterior cruciate ligament resulted in an increase of anterior drawer in flexion and extension. External and internal rotation were increased in both flexion and extension. Hyperextension also was increased. It is suggested that the AMB of the anterior cruciate is responsible for the increase in antero posterior drawer with flexion. The selective cutting of the posterior cruciate ligament demonstrated that it is important in the flexed knec and produces an increased poste rior drawer measurement with no change in anterior drawer sign. Rotational stability was unchanged in extension, but altered in flexion after cutting the posterior cruciate.