PURPOSE: As a baseline study for clinical application, we investigated MRI findings of normal cruciate ligaments in the knee being flexed as compared to those in the knee being extended. MATERIALS AND METHODS: Seven asymptomatic volunteers were studied. Knee MRI was performed with a 1.5 Tesla unit using a dual 3 inch coil. Inthe decubitus position, sagittal scanning was performed with the knee in extension, and subsequently, in flexion. We observed the shape and signal intensity of both cruciate ligaments, and measured the angles between the longaxis of the femur and ligaments, and the ligament dimensions in extension and flexion images. RESULTS: As flexionand extension images were compared, cruciate ligaments differed both in their appearance and dimensions. With flexion, joint space was widened, PCL became straightened and the signal intensity of ACL became homogeneously low; both cruciate ligaments became longer and thinner. These MRI findings were statistically significant except forthinning of PCL. CONCLUSION: MRI appearance and the dimensions of cruciate ligaments were different in the flexed knee as compared to those in the extended knee.