Clinical, radiographic and pathologic abnormalities in calcium pyrophosphate dihydrate deposition disease (CPPD) (pseudogout) are outlined in an investigation of 85 patients with definite or probable disease and available cadaveric and human surgical material. Pyrophosphate arthropathy produced distinctive roentgenographic abnormalities with were most frequent in the knee, wrist and metacarpophalangeal joints. Although the alterations superficially resembled osteoarthritis, they were frequently more severe and progressive with extensive fragmentation of bone, causing intra-articular osseous bodies. Pyrophosphate arthropathy occurred in unusual locations, such as the radiocarpal compartment of the wrist, elbow, and patellofemoral compartment of the knee. These characteristics allow the radiologist to suggest a probable diagnosis of CPPD even in the absence of articular calcification.