Background and purpose:  To estimate the diagnostic accuracy of cardiac 123I‐metaiodobenzylguanidine (MIBG) scintigram for detection of Parkinson disease. Methods:  A cross‐sectional study with index test of MIBG scintigram and reference standard of U.K. Parkinson’s Disease Brain Bank Criteria was performed in 403 patients. Ratio of cardiac‐to‐mediastinum MIBG accumulation was determined at 20 min (early H/M) and 4 h (late H/M). Area under the receiver‐operator characteristic (ROC) curve, sensitivity and specificity in detecting Parkinson disease were analyzed. Accuracy was analyzed in a subgroup of patients with disease duration of 3 years or less. Results:  Area under the ROC curve was 0.89 using either early or late H/M as a diagnostic marker (95% CI 0.85–0.92 for early H/M and 0.86–0.93 for late H/M). Sensitivity and specificity were 81.3% (76.1–85.8%) and 85.0% (77.7–90.6%) for early H/M and 84.3% (79.3–88.4%) and 89.5% (83.01–94.1%) for late H/M. In the subgroup with duration of 3 years or less, the ROC curve area, sensitivity, and specificity were 0.86 (0.79–0.92), 76.0% (64.8–85.1%), and 83.9% (71.7–92.4%) for early H/M and 0.85 (0.78–0.92), 73.3% (61.9–82.9%), and 87.5% (75.9–94.8%) for late H/M. Conclusion:  Although diagnostic accuracy of cardiac MIBG scintigram is high, it is limited because of insufficient sensitivity in patients with short duration.