The role of preventive treatment in the management of migraine must be reassessed. Many patients who would benefit from preventive therapy do not receive it, and many might benefit from earlier and more aggressive use of preventive therapy. Physicians who treat migraine have long recognized that a subset of patients with episodic migraine evolve to chronic forms of the disorder that are difficult to treat and have a poor outcome. This article reviews the evidence for current and emerging prophylactic migraine treatment and raises the possibility that timely use of prophylactic treatment might modify or prevent the transformation to chronic migraine and the extreme disability that characterizes a small but significant subset of the migraine population. Along with aggressive treatment of the acute pain and other symptoms of migraine, prevention of progression to severe forms of this disorder will increasingly be a focus and goal of the treatment.