The arterial supply to the patella has been studied in 21 specimens. Fifteen were obtained at autopsy and six at amputation. Nine of the specimens were normal, six were diagnosed as chondromalacia patellae and six as osteoarthrosis. Micropaque was injected into the arteries, and the Spalteholtz clearing technique was used. Radiography was also performed. In addition to previously reported observations, arteries were found to penetrate into the patella from the interior of the quadriceps tendon, from the synovial tissue and from the medial and lateral retinaculae. Moreover, it was found that with increasing degree of cartilage destruction the arterial pattern within the patella became disturbed and irregular with formation of anastomoses.