Posteroanterior weight-bearing radiographs, made with the knee in 45 degrees of flexion, were compared with conventional radiographs for fifty-five patients who had surgical treatment for a lesion causing pain in one knee. Narrowing of the cartilage space of two millimeters or more was defined as indicative of major degeneration (grade III or IV). Comparison of the intraoperatively observed degeneration with the narrowing that was seen on the radiographs revealed that the posteroanterior weight-bearing radiographs that were made with the knee in 45 degrees of flexion were more accurate (p less than 0.01), more specific (no false-positives) (p less than 0.01), and more sensitive (fewer false-negatives) than the conventional extension weight-bearing anteroposterior radiographs.