The aim of this study was to determine the value of scaphoidtrapezium osteoarthritis (ST osteoarthritis) as an early sign of calcium pyrophosphate dihydrate disease (CPDD) in a cohort of patients undergoing surgery for osteoarthritis of the first carpometacarpal joint. We examined whether patients with cartilage calcification of the wrist at the time of operation had ST osteoarthritis, indicating CPDD at an earlier time (retrospective study), and whether patients with ST osteoarthritis but without cartilage calcification at the time of surgery develop radiological or clinical signs of CPDD at a later time (prospective study). From 1 January 1989 to 31 December 1995 a total of 169 patients (from an orthopaedic clinic) with a diagnosis of osteoarthritis of the first carpometacarpal joint were included in the study; 167 underwent surgery and two were treated without. Of the 16 patients showing calcification on surgery and therefore included in the retrospective study, 12 had prior radiographs, of which eight showed ST osteoarthritis. Among these, four had no concomitant cartilage calcification in the prior radiographs. Of the 32 patients in the prospective group having ST osteoarthritis but no calcifications at the time of surgery, 27 could be clinically examined. Of these, two showed cartilage calcifications on the follow-up radiographs of the hands. The presence of ST osteoarthritis is a helpful diagnostic finding for the diagnosis of CPDD, especially in cases without radiographic cartilage or fibrocartilage calcification of the wrist. ST osteoarthritis may then point to the correct diagnosis.