Compared to the general population, Parkinson's disease (PD) patients have a higher risk of hip fracture and secondary osteoporosis. In the general population, it is known that physical performance is related to bone density. However, the relationship between bone density and physical performance in ambulatory PD patients has not been studied. This study investigated the relationship between bone density and physical performance in ambulatory PD patients. Fourteen ambulatory PD patients (9 men and 5 women; mean age, 67.3±7.7 years; Hoehn & Yahr stages 1–3) were enrolled. Bone density of the right calcaneus was assessed using a speed of sound (SOS) ultrasound measurement device. Disease severity was categorized using the Japanese Unified Parkinson Disease Rating Scale (UPDRS). Furthermore, to assess physical performance, lower extremity strength, 10 m gait time, and body sway were measured. Since SOS is strongly affected by age and gender, it was standardized by the patient's age and gender, and the t-score was calculated with the use of SOS. Significant correlations were found between the t-score and UPDRS,lower extremity strength, and 10 m gait time. When the 4 parts of the UPDRS were analyzed separately, only the correlation between part IV and the t-score was not significant. The findings of this study suggest that higher disease severity and weaker lower extremity physical performance decreased bone density in ambulatory PD patients. Therefore, in order to prevent hip fractures in ambulatory PD patients, assessing the UPDRS and lower extremity physical performance may be clinically useful.