In eleven patellae excised from patients with the clinical condition “chondromalacia patellae” the following constant pathological changes are seen: (1) hyperplasia of the chondrocytes, with vascularization and advancing ossification into the deep zone of the articular eartilage; (2) new bone formation and thinning of the subchondral osseous plate; (3) focally or diffusely severe osteoporosis of the trabecular bone. In some cases we have observed superficial fibrillation of the cartilage and discreet nodular aggregates of woven bone on osteoporotic trabeculae. Radioisotope bone scans confirmed disordered calcium metabolism in this condition. The over-all findings do not support the concept that the clinical condition known as chondromalacia patellae is due to osteoarthrosis or primary cartilaginous degeneration.