In forensic medicine, classic autopsy is sometimes insufficient to determine the true cause of death, and in these cases additional laboratory tests have to be carried out. In addition to the toxicological, histopathological microscopic examination, and molecular diagnostics, biochemical laboratory analyses are used to help determine the cause of death. Determining the concentration of certain biochemical markers in body fluids can clarify the time and cause of death or the systemic pathophysiological changes in the dying process. Samples used in biochemical examinations include blood and urine and / or other biological fluids (the vitreous, pericardial and cerebrospinal fluid). Diabetes mellitus, or its sometimes fatal complication diabetic ketoacidosis, which occurs due to the accumulation of ketones in the blood, is one of the conditions that can lead to sudden death and has thus become the subject of forensic medicine. 30 million people around the world are suffering from diabetes, and it is one of the leading causes of death in developed countries. Obesity and aging of populations drive an increase in these conditions. In a significant percentage of people diabetes is not recognized as a disease because it is difficult to diagnose until clinical symptoms become apparent and complications appear. It is also difficult to identify diabetes mellitus as a complication leading to death without additional laboratory examinations. One of the postmortal biochemical markers, whose determination can greatly assist in determining diabetes and ketoacidosis as a cause of death, is the product of the ketoacidosis-the ketone body, β-hydroxybutyrate or β-hydroxysaturic acid. This acid is an anion, and its increase in blood results in a decrease in the pH of the organism leading to ketoacidosis. In ketoacidosis, β-hydroxybutyrate represents 65-75% of the total concentration of ketone bodies. The β-hydroxybutyrate concentration can be determined from a variety of biological samples such as blood, urine, vitreous, cerebrospinal, pericardial and synovial fluid, and liver homogenates. The values of β-hydroxybutyrate in certain biological samples are in good correlation. It is a stable compound whose values do not change with decomposition. For this reason, β-hydroxybutyrate levels can be considered an appropriate biochemical parameter to estimate the β-hydroxybutyrate concentration at the time of death, thus confirming or disproving ketoacidosis as a cause of death.