SummaryThe authors looked at the association of illness duration and acute treatment response in 1,087 patients with unipolar major depression. Three treatment groups were compared, including a group that received electroconvulsive therapy (ECT), a group that received antidepressants, and a group receiving neither ECT nor antidepressants. Up to an illness duration of 2 years, treatment was significantly associated with recovery; ECT produced significantly better results than other treatments. However, when the illness had lasted >2 years, the ECT‐treated group showed a significant decline in recovery, and ECT was no longer superior to other treatments. We conclude that duration of illness at index hospitalization has an important influence on treatment response rates and the likelihood of recovery by hospital discharge.