The efficacy of flunarizine in migraine prophylaxis is confirmed in both open and controlled trials. However, it is unknown what factors may influence a good response to prophylaxis with flunarizine. The aim of this study was to determine the possible predictive factors for therapeutic responsiveness to 3 months' treatment with flunarizine. One-hundred headache patients treated with flunarizine were evaluated. We considered "responders" those patients who recorded a reduction in migraine frequency of 75% after treatment. Statistical analysis revealed four factors which might influence therapeutic responsiveness in our patients. Positive factors were a family history (p<0.01) and high intensity of pain (p<0.01); negative factors were frequent attacks (p<0.01) and a history of analgesic abuse (p<0.001). Patients with no previous history of analgesic abuse, low frequency of attacks at baseline, higher levels of migraine pain, and positive family history constitute the prototype of flunarizine long-term treatment responders.