The recent deaths of nine people in Japan, in October 2004, apparently in two suicide pacts1—seven suicides in one pact and two in the other—have brought the relatively rare phenomenon of suicide pacts into the limelight. What is unusual is that these pacts seem to have been arranged between strangers who met over the internet and planned the tragedy via special suicide websites. This is in contrast to traditional suicide pacts, in which the victims are people with close relationships.

A suicide pact is an agreement between two or more people to commit suicide together at a given place and time. In England and Wales, for epidemiological purposes, people who have committed suicide within three days of each other in the same registration subdistrict are considered potential victims of a suicide pact.2 A related phenomenon is homicide-suicide, in which a person commits a murder and then ends his or her own life. Dyadic death is a term that encompasses both suicide pacts and homicide-suicides.3 A suicide …