To supplement the traditional ICHD-2 diagnosis for migraine with aura (MA) we developed a diagnostic scale for migraine aura that quantifies the importance of the cardinal characteristics of MA. Since more than 99% of MA patients have visual aura, we developed for simplicity a Visual Aura Rating Scale (VARS). In total 427 patients with MA (ICHD-2) or nonaura visual disturbances were diagnosed in a validated semistructured interview by a trained physician. The patients were separated into a derivation sample and a validation sample. By regression analysis we identified the visual aura characteristics associated with MA in the derivation sample. Based on the identified characteristics we developed VARS and derived a predictive VARS score which was tested in the validation sample. The VARS score is the weighted sum of the presence of five visual symptom characteristics: duration 5-60 min (3 points), develops gradually > or = 5 min (2 points), scotoma (2 points), zig-zag lines (2 points), and unilateral (1 point). The maximum score is 10 points. A VARS score of 5 or more diagnosed MA with a sensitivity of 96% (95% CI 92-99%) and a specificity of 98%(95% CI 95-100%) in the derivation sample, and a sensitivity of 91% (95% CI 86-95%) and a specificity of 96% (95% CI 91-100%) in the validation sample. VARS adds evidence based weights to a number of clearly specified characteristics; it is easy to learn, apply and teach and may therefore be a valuable addition to traditional ICHD-2 diagnosis.