Radiographic features of calcium pyrophosphate dihydrate (CPPD) crystal deposition disease are outlined in an investigation of 32 patients, with definite or probable disease (according to the diagnostic criteria previously utilized by McCarty). The crystal deposits within fibro- and hyaline cartilage (chondrocalcinosis) may produce an acute synovitis (pseudogout syndrome), and in some patients a radiographically distinctive degenerative arthropathy (pyrophosphate arthropathy). These abnormalities are most frequent in the knee, wrist and symphysis pubis, but often other joints may be affected. Although the alterations superficially resemble osteoarthritis, they are more severe and progressive (Charcot-like joint).