There is only limited information available on the sagittal alignment of the lower extremity of normal subjects under weight-bearing conditions. Our aim was to determine the sagittal alignment of the lower extremity under such conditions. Anteroposterior and lateral radiographs were taken of the 20 lower extremities of 20 healthy female volunteers while standing. The coronal mechanical axis passed through 29% medial to the proximal tibial articulating surface. The sagittal mechanical axis passed through 44% anterior to the distal femoral condyle and 33% anterior to the proximal tibial articulating surface, and also passed 3 mm anterior to the intercondylar notch. Our study showed that the coronal and sagittal mechanical axes of the lower extremity do not always pass through the center of the knee. Our results will provide important information for alignment in surgery of lower extremity such as knee arthroplasty and osteotomy.