The aim of the present study was to compare the collagenous fibre systems of the anterior (ACL) with the posterior cruciate ligament (PCL). 22 cruciate ligaments were examined by the combined use of light-, transmission- and scanning electron microscopy. Characteristic interligamental differences were established. ACL: more anchoring type VI collagen, thinner but more branched fibrils, complex collagen networks, much more elastic elements. PCL: more type IV collagen, many intrinsic vessels, thicker fibrils, parallel fibre arrangement. The results indicate that the ACL is exposed at the first line to rotational forces, the PCL probably more to tensional forces. The collagen fibre arrangement of the cruciate ligaments is to take into consideration by the surgeon.