Background Diagnosing when someone is in the last days of their life is an ongoing difficulty for clinicians. There is often significant clinical uncertainty and modern medical science is poor at predicting how or when patients will die.

Aim To review the literature to assess the knowledge of the biology of dying - excepting sudden death.

Method A systematic review of the biology of dying excepting sudden death was performed. 2661 articles on MEDLINE and 3360 articles from EMBASE were identified. Titles and abstracts from each database were examined independently for relevance.

Results 18 articles were identified. Interleukin-2 is preferentially expressed in brainstem neuronal centres in critically ill aging adults and infant patients dying from various conditions. A number of papers suggested that there may be a final common pathway to dying.

Conclusion There are few studies investigating the biological changes during dying. Research into this area could have a potential impact on a dying persons care.