Sudden death is now currently described as natural unexpected death occurring within 1h of new symptoms. Most studies on the subject focused on cardiac causes of death because most of the cases are related to cardiovascular disease, especially coronary artery disease. The incidence of sudden death varies largely as a function of coronary heart disease prevalence and is underestimated. Although cardiac causes are the leading cause of sudden death, the exact incidence of the other causes is not well established because in some countries, many sudden deaths are not autopsied. Many risk factors of sudden cardiac death are identified: age, gender, heredity factors such as malignant mutations, left ventricular hypertrophy and left ventricle function impairment. The role of the police surgeon in the investigation of sudden death is very important. This investigation requires the interrogation of witnesses and of the family members of the deceased. The interrogation of physicians of the rescue team who attempted resuscitation is also useful. Recent symptoms before death and past medical history must be searched. Other sudden deaths in the family must be noted. The distinction between sudden death at rest and during effort is very important because some lethal arrhythmia are triggered by catecholamines during stressful activity. The type of drugs taken by the deceased may indicate a particular disease linked with sudden death. Sudden death in the young always requires systematic forensic autopsy performed by at least one forensic pathologist. According to recent autopsy studies, coronary artery disease is still the major cause of death in people aged more than 35 years. Cardiomyopathies are more frequently encountered in people aged less than 35 years. The most frequent cardiomyopathy revealed by sudden death is now arrhythmogenic right ventricular cardiomyopathy also known simply as right ventricular cardiomyopathy (RVC). The postmortem diagnosis of cardiomyopathies is very important because the family of the deceased will need counseling and the first-degree relatives may undergo a possible screening to prevent other sudden deaths. In each case of sudden death, one important duty of the forensic pathologist is to inform the family of all autopsy results within 1 month after the autopsy. Most of the recent progress in autopsy diagnosis of sudden unexpected death in the adults comes from molecular biology, especially in case of sudden death without significant morphological anomalies. Searching mutations linked with functional cardiac pathology such as long-QT syndrome, Brugada syndrome or idiopathic ventricular fibrillation is now the best way in order to explain such sudden death. Moreover, new syndromes have been described by cardiologists, such as short-QT syndrome and revealed in some cases by a sudden death. Molecular biology is now needed when limits of morphological diagnosis have been reached.