Electroconvulsive therapy (ECT) is the most effective treatment for severe depression, but is associated with cognitive side effects. Side effects on executive function and memory may persist for months. Patients with a low cognitive reserve and/or poor cognition before ECT seem to be at greater risk of cognitive side effects than patients with a high cognitive reserve. However, better understanding of the nature and predictors of these side effects is needed. We recommend implementing a cognition assessment tool to monitor cognition during ECT. This may improve patient information and provide a basis for more personalised treatments.