Depression is a common disorder in later life. The prevalence of depression in aged nursing home patients in 36 studies in various countries was reviewed. Results show prevalence rates ranging from 2% to 61%. Average prevalences were calculated for depressive symptoms, minor depression and major depression each. The averages thus found are 43.9% for depressive symptoms, 25.7% for minor depression and 15.5% for major depression. In order to find an explanation for the variation in occurrence of depression in nursing homes, factors that may have influenced the results are described. Both the definition of depression and the kind of instrument used in measuring depression appear to be highly responsible for the variations found.