In terms of medicine and law, death occurs by ceasing the function of the brain stem, in which there are respiratory control centers and cessation centers of the heart, the normal function of which is crucial for the functioning of the rest of the organism. Determining the cause of death often also determines the manner of death, natural or violent death. An autopsy is the only sure way to determine the cause of sudden or sudden unexplained natural death, and the autopsy report is the only one acceptable for use for legal purposes and for subsequent analysis (expert opinion). The study included all persons who died from natural causes, determined by autopsy at the Institute of Forensic Medicine and Criminalistics Rijeka in the period from 2015 to 2019. Of the necessary parameters, sex, age and organic systems were used. The highest number of natural deaths was recorded in 2017, while according to 2019 a downward spiral was observed. Of the 605 people who died of natural causes, 437 were male (71%), while the remaining 175 were female (29%). In terms of age, the majority are in older age groups such as the 61-70 age group with 160 (26%) and 71-80 with 152 (25%) recorded fatality. The largest number of natural deaths was caused by diseases from the group of diseases of the circulatory system (I00-I99) with 495 (82%) deaths. The following are diseases of respiratory system (J00-J99) with 34 (6%), diseases of the nervous system (G00-G99) with 26 (4%), diseases of the digestive system (K00-K99) with 24 (4%) and neoplasms (C00-D48) with 20 (3%) reported deaths. The group "other diseases and conditions" represents other organic systems whose diseases, as well as certain conditions, record only 6 (1%) deaths.