The aim of this study was to test the precision and reliability of measurements of the bone mineral density (BMD) of the trapezium in patients with osteoarthritic trapeziometacarpal joints using dual-energy X-ray absorptiometry scans and to assess whether there is an acceptable correlation between the BMD of the trapezium and that of the distal radius, for which normative data exist. We included 66 patients (52 women, 14 men) diagnosed with Eaton–Glickel stage II–IV osteoarthritis and a mean age of 59 years (range 40–77) in a prospective study. We found good intra- and inter-observer agreement of BMD measurements. Reliability was also good in repeated measurements. There was an indication of an increase in BMD with progression in the Eaton–Glickel stage. There was only a moderate correlation between the BMD of the trapezium and that of the radius.