Bone mineral density (BMD) in 22 patients (three females, 19 males, aged 58-76 years) with idiopathic Parkinson's disease (PD) was measured by dual photon absorptiometry (DPA) using a M&SE OsteoTech 300 scanner. The BMDs of the 2nd to 4th lumbar vertebrae were measured and the mean density was presented as g cm-2. The BMD of the PD patients was compared with normal BMD values within the same age groups, and the patients were interpreted as normal, suffering mild osteoporosis or severe osteoporosis. The patients were divided into two groups according to (a) the Hoehn and Yahr (H-Y) scale as high or low, or based on (b) the duration of the disease as long or short, for comparison. The prevalence of abnormal BMD in each subgroup of patients was calculated. The results show that the BMD of all the PD patients was lower than those of the normal controls. The PD patients with a high H-Y scale had a higher prevalence of severe osteoporosis. However, the difference between any two groups, separated by the two criteria, is not significant by Fisher's test. We find that PD patients have a higher incidence of severe osteoporosis.