Although previous studies showed that patients with Parkinson's disease (PD) have low bone mineral density (BMD), there is little data on factors predisposing PD patients to low BMD. We compared the BMD of 108 PD patients (58 females) with an average age of 68 (range 42-83) years with that of 216 sex- and age-matched controls, adjusting for other covariate factors (exercise levels, estrogen status, dietary calcium intake, smoking, drinking, body mass index, and percentage of body fat). The mean BMD in the hip and lumbar spine of male PD patients did not differ significantly from those of male controls. On the other hand, the mean BMD in femoral neck was significantly lower in female PD patients than in controls (0.53 +/- 0.11 g/cm(2) versus 0.58 +/- 0.10 g/cm(2), P = 0.005). Compared with controls, female PD patients experienced menopause much earlier (47 years versus 50 years, P = 0.028). The percentage of body fat was also lower in female PD patients (33% versus 36%, P = 0.02). A lower BMD in the hip in female PD patients was associated with an increased number of months after menopause (P = 0.004) and lower percentage of body fat (P = 0.025). We concluded that female patients with PD have lower hip BMD, but this association appears largely attributable to differences in percentage body fat and years since menopause. After multivariate adjustment, PD no longer remained independently associated with reduced BMD in female patients.