The anterior cruciate ligament (ACL) consists of an anteromedial bundle (AMB) and a posterolateral bundle (PLB). A reconstruction restoring the functional two-bundled nature should be able to approximate normal ACL function better than the most commonly used single-bundle reconstructions. Accurate tunnel positioning is important, but difficult. The purpose of this study was to provide a geometric description of the centre of the attachments relative to arthroscopically visible landmarks. The AMB and PLB attachment sites in 35 dissected cadaver knees were measured with a 3D system, as were anatomical landmarks of femur and tibia. At the femur, the mean ACL centre is positioned 7.9 +/- 1.4 mm (mean +/- 1 SD) shallow, along the notch roof, from the most lateral over-the-top position at the posterior edge of the intercondylar notch and from that point 4.0 +/- 1.3 mm from the notch roof, low on the surface of the lateral condyle wall. The mean AMB centre is at 7.2 +/- 1.8 and 1.4 +/- 1.7 mm, and the mean PLB centre at 8.8 +/- 1.6 and 6.7 +/- 2.0 mm. At the tibia, the mean ACL centre is positioned 5.1 +/- 1.7 mm lateral of the medial tibial spine and from that point 9.8 +/- 2.1 mm anterior. The mean AMB centre is at 3.0 +/- 1.6 and 9.4 +/- 2.2 mm, and the mean PLB centre at 7.2 +/- 1.8 and 10.1 +/- 2.1 mm. The ACL attachment geometry is well defined relative to arthroscopically visible landmarks with respect to the AMB and PLB. With simple guidelines for the surgeon, the attachments centres can be found during arthroscopic single-bundle or double-bundle reconstructions.