A series of 22 cases of fatal accidental or suicidal hypothermia is presented. Necropsy findings on which the diagnosis can be based were analysed. Purple skin and swelling of face, hands and feet, as well as violet patches on elbows or knees were the most frequent external signs (Frequency 54--59%). The most conspicuous internal macroscopic signs were gastric erosions or haemorrhages, which were seen in half of the cases. Other less frequent signs were pulmonary oedema and acute renal and hepatic degeneration. Microscopically the myocardium showed small degenerative foci and/or fuchsinophilic fibres in two thirds of the cases. The myocardium was macroscopically normal. Histamine and serotonin assays from urine did not indicate increased excretion during exposure. Catecholamine concentrations in urine were high (greater than 0.1 mug/ml) in most hypothermia deaths indicating increased excretion due to cold. The best diagnostic signs seem to be purple skin and oedema in face and ears, stomach erosions, degenerative foci in myocardium and high concentration of catecholamines in the urine.