Scapholunate advanced collapse (SLAC) is a pattern of wrist malalignment that has been attributed to posttraumatic or spontaneous osteoarthritis of the wrist. Its features, however, also have been observed in patients with idiopathic calcium pyrophosphate dihydrate (CPPD) crystal deposition disease. To determine the frequency and characteristics of SLAC in this disease, the authors reviewed wrist radiographs in 168 well-documented cases of this disorder. Forty-four of the cases (26%) revealed wrist abnormalities typical of SLAC. Associated findings included bilateral involvement (63%); calcification in or near the triangular fibrocartilage (70%); scapholunate widening or dissociation (70%); and arthropathies of the trapezioscaphoid (57%), metacarpophalangeal (second through fifth) (52%), first carpometacarpal (40%), and radiolunate (14%) joints. Results strongly suggest that CPPD crystal deposition disease is one of the major causes of SLAC. Furthermore, radiolunate arthropathy was found in 14% of the patients with SLAC and CPPD crystal deposition disease, which is different from other observations.