Background: It has been stated that rates of homicide due to mental disorder are constant over time. Aims: To examine whether there were changes in the rates of homicide due to mental disorder over time, and whether changes in these rates were associated with changes in the rates of other homicides in England and Wales. Method: Examination of four sets of official homicide statistics from England and Wales from 1946 to 2004. Results: The rate of total homicide and the rate of homicide due to mental disorder rose steadily until the mid-1970s. From then there was a reversal in the rate of homicides attributed to mental disorder, which declined to historically low levels, while other homicides continued to rise. Conclusions: The reasons for the rise and fall in homicides attributed to mental disorder are not clear. The earlier increase in such homicides may have been due to the same sociological factors that caused the increase in other homicides over that time. The subsequent decline may have been due to improvements in psychiatric treatments and service organisation. Another possibility is that there has been an informal change to the legal tests for the finding of homicide due to mental disorder.