Background: Many people with depression in residential care homes for the elderly do not receive treatment because their depression remains undetected. Aims: To determine the effects of staff training on the detection, treatment and outcome of depression in residents of ten homes. Method: We conducted a randomised controlled trial in ten residential homes. The intervention consisted of a training programme for staff and collaborative evaluation by staff and a mental health specialist of residents with possible depression. Results: Recognition of depression increased more in homes where staff received the training than in the control homes. Treatment rates also increased compared with control homes, but the increase was not significant. Residents with depressive symptoms had a more favourable course when staff had received training. Moreover, the prevalence of depressive symptoms decreased, but the decrease was not significant. Conclusions: Training of care staff results in the increased detection of depression in the elderly, a trend towards more treatment and better outcomes.