The diagnosis of death caused by hypothermia can often only be made by exclusion. In this article, we discuss the significance of rectal temperature determination at the death scene for establishing the diagnosis of fatal hypothermia. Six cases of fatal hypothermia subjected to medico-legal autopsy at the Institute of Legal Medicine, Hamburg, Germany, were reviewed. Findings at external examination, autopsy findings with special regard to characteristics hypothermia-related changes, histological findings, and toxicology results were analyzed. In all cases investigated, a discrepancy between a low rectal temperature and other parameters for estimation of the time since death such as still displaceable postmortem lividity and electrical excitability of skeletal muscles was present, leading to the prompt suspicion of fatal hypothermia at the medico-legal death scene investigation. An early death scene investigation by a forensic specialist is of striking importance for establishing the correct diagnosis, because this discrepancy can only be observed in the early postmortem interval.