The aim of this study was to evaluate 123I-meta-iodobenzyl guanidine (123I-MIBG) myocardial scintigraphy in patients with Parkinson's disease as a way of detecting cardiac sympathetic dysfunction, and comparing the stage of disease and intensity of drug treatment with accumulation of 123I-MIBG. 123I-MIBG myocardial scintigraphy was performed in 48 patients with Parkinson's disease and 25 control subjects. In the planar imaging studies, the data acquisition matrix was 256 x 256 and the preset time was 5 min. The heart-to-mediastinum (H/M) average count ratio was calculated for both early (15 min) and delayed (3-4 h) images after 123I-MIBG injection (111 MBq). The mean H/M ratio in patients with Parkinson's disease was significantly lower than that in the controls (P < 0.0001). Regardless of disease severity, intensity of anti-Parkinson treatment and the presence or absence of orthostatic hypotension, the mean H/M ratios were always low in the Parkinsonian patients. Parkinson's disease may result in a severe abnormality of cardiac sympathetic function which has not been detected by previous cardiovascular autonomic studies.