The aim of this study was to examine the pathoplastic effects of childhood parental separation experiences on depressive symptoms. Patients with acute major depression were identified in a large 31-center study of affective disorders in Japan. Information regarding the patients' childhood losses was collected using a semistructured interview, and their depressive symptomatology was assessed by the Center for Epidemiologic Studies Depression Scale (CES-D). Patients reported significantly higher CES-D total scores when they had experienced early object loss of the same-sex parent. In terms of the CES-D subscores derived by factor analysis, early object loss significantly aggravated symptoms that people normally could cope with but could no longer cope with when depressed (e.g. 'poor appetite', 'cannot shake off the blues' and 'everything an effort.'). Once depression develops, early object loss may act as a pathoplastic factor by making it severer especially by rendering people less able to perform what they normally could do.