Background There is an established link between depression and interest in hastened death in patients who are seriously ill. Concern exists over the extent of depression in patients who actively request euthanasia/physician-assisted suicide (PAS) and those who have their requests granted.

Objectives To estimate the prevalence of depression in refused and granted requests for euthanasia/PAS and discuss these findings.

Methods A systematic review was performed in MEDLINE and PsycINFO in July 2010, identifying studies reporting rates of depression in requests for and cases of euthanasia/PAS. One author critically appraised the strength of the data using published criteria.

Results 21 studies were included covering four countries. There was considerable heterogeneity in methods of assessing depression and selecting patients. In the highest quality studies, in the Netherlands and Oregon, 8–47% of patients requesting euthanasia/PAS had depressive symptoms and 2–17% of completed euthanasia/PAS cases had depressive symptoms. In the Netherlands, depression was significantly higher in refused than granted requests, and there was no significant difference in the rate of depression between euthanasia cases and similar patients who had not made a request for euthanasia.

Conclusion It is unclear whether depression increases the probability of making a request for euthanasia/PAS, but in the Netherlands most requests in depressed patients are rejected, leaving a depression rate in cases that is similar to the surrounding population. Less evidence is available elsewhere, but some level of depression has been identified in patients undergoing euthanasia/PAS in all the countries studied. Whether the presence of depression is ever compatible with an ethical decision on euthanasia/PAS is discussed.