OBJECTIVES: Depression is a prevalent and debilitating disorder, often undiagnosed. Patients may present with a broad range of symptoms including mood, somatic and painful symptoms. Our aim was to create a comprehensive symptom checklist to guide questionnaire development for the diagnosis and outcomes assessment of depression. METHODS: A systematic literature review was conducted to list all emotional, somatic and painful physical symptoms from validated scales in depression. One hundred fifty semi-structured interviews were conducted with 50 clinicians, 50 patients with diagnosed depression (DEP) and 50 patients with physical symptoms of depression, referred to by physicians as masked depression (MD) and Somatoform disorders, in France, Germany, Italy, Spain and the UK. The clinicians were asked to describe their patients' symptoms, the profiles of DEP and MD patients, and to comment and rate the listed symptoms for DEP and MD patients. The patients were asked to describe their symptoms, to comment and rate the listed symptoms. RESULTS: Twenty-two validated scales covering symptoms of depression were reviewed. Two lists of symptoms were created: one including medical terms for clinician interviews, and one including lay terms for patient interviews. Although clinician interviews tend to show differences between DEP and MD patients, the majority of symptoms were reported to exist in both groups. Moreover, patients' reports showed fewer differences between DEP and MD than clinicians' reports. Overall, the results were comparable between countries. The final checklist covers nine emotional symptoms and 37 somatic symptoms in nine groups (gastrointestinal, cardiopulmonary, neurological, neuropsychological, neuromuscular, urogenital, pain, sleep, autonomic system). CONCLUSIONS: The checklist is the first comprehensive description of symptoms of depression, including emotional, somatic and painful physical symptoms. This checklist will guide further instrument development for the diagnosis and outcomes assessment of depressed patients.