In an 11-country European collaboration, 14 population-based surveys included 21,724 subjects aged > or = 65 years. Most participating centres used the Geriatric Mental State (GMS), but other measures were also used. To derive from these instruments a common depression symptoms scale, the EURO-D, to allow comparison of risk factor profiles between centres. Common items were identified from the instruments. Algorithms for fitting items to GMS were derived by observation of item correspondence or expert opinion. The resulting 12-item scale was checked for internal consistency, criterion validity and uniformity of factor-analytic profile. The EURO-D is internally consistent, capturing the essence of its parent instrument. A two-factor solution seemed appropriate: depression, tearfulness and wishing to die loaded on the first factor (affective suffering), and loss of interest, poor concentration and lack of enjoyment on the second (motivation). The EURO-D scale should permit valid comparison of risk-factor associations between centres, even if between-centre variation remains difficult to attribute.