Duchenne muscular dystrophy (DMD) is one of the most common and severest muscular dys-trophies. Although it can be a cause of death when associated with cardiac muscle and/or respiratory muscles, no cases of sudden deaths in the setting of undiagnosed DMD with car-diac involvement have been reported in the literatures. Previous studies showed that N-ter-minal-proBNP (NT-proBNP) was a robust laboratory biomarker to diagnose and monitor cardiac failure in clinical situations, suggesting that it may be used as an auxiliary indicator for diagnosis on left ventricular dysfunction in sudden cardiac deaths in forensic settings. Here, we reported a case of 29-year-old man who died suddenly. Autopsy revealed that muscles of the body were almost replaced by fatty and fibrotic tissues. The heart was enlarged with dis-array and degeneration of cardiomyocytes in cardiac muscle. Total absence of dystrophin was detected by immunohistochemical staining, which confirmed DMD. Postmortem biochemical test of pericardial fluid revealed a high level of NT-proBNP, indicating dysfunction of the left ventricle before death. The cause of death was certified as an early dilated cardiomyopathy (DCM)/dysfunction of the left ventricle secondary to DMD, suggesting that sudden cardiac death with cardiac dysfunction could be identified by immunohistochemical method in com-bination with pericardial fluid NT-proBNP determination after systemic autopsy.