The aim of this study was to assess whether a cut-off of five on the 15-item version of the Geriatric Depression Scale (GDS) that was determined beforehand yielded the best sensitivity and specificity for the diagnosis of major depression in the elderly in primary care. A sample of 330 patients was drawn from a group of elderly patients (≥ 55 years) that participated in a clinical trial, the West-Friesland Study (WFS). The mood-module of the PRIMary care Evaluation of Mental Disorder (PRIME-MD) served as the external criterion for major depression. The results showed that using a ROC-curve the best cut-off score of the GDS-15 was five. This cut-off score gave a sensitivity of 0.79 and a specificity of 0.67 and a negative predictive value of 0.94. It is concluded that the validation in retrospect of the a priori chosen cut-off score of five in a sample of the study population supports our a priori choice.