Cluster headache is a rare, severe, clinically well-characterized disorder that occurs in both episodic and chronic forms. The painful short-lived attacks occur unilaterally and are associated with signs and symptoms of autonomic involvement. They are difficult to treat, and reported prophylactic therapies include ergotamine, steroids, methysergide, lithium carbonate, verapamil, valproate, capsaicin, leuprolide, clonidine, methylergonovine maleate, and melatonin. Baclofen, an antispastic agent, has been shown to have an antinociceptive action. Its efficacy in the treatment of neuralgias, central pain following spinal lesions or painful strokes, migraine, and medication misuse chronic daily headache suggested that it may prevent cluster headache attacks. Nine cluster headache patients received baclofen, 15 to 30 mg, in three divided doses. Within a week, six of nine patients reported the cessation of attacks. One was substantially better and became attack free by the end of the following week. In the remaining two patients, the attacks worsened and corticosteroids were prescribed. In this pilot study, baclofen seemed to be effective and well tolerated for the prevention of cluster headache.