Cluster headaches are rare in childhood. We identified 35 patients with cluster headaches starting at or before 18 years of age, including 7 patients with onset prior to age 10. All patients met the criteria of the International Headache Society for episodic or chronic cluster headaches. Patients experienced cluster headaches for as long as 20 years before seeking medical attention and required many medical contacts to establish the correct diagnosis. The clinical features of cluster headaches during childhood were similar to those which typically occur in adult life. Cluster headache patterns changed over 18 years of follow up. The frequency and duration of cluster periods increased in 14 subjects. The frequency of single headache attacks during cluster periods also increased in a similar number of subjects. We conclude that cluster headaches starting in childhood or adolescence closely resemble the adult form of the disease. In many patients, the frequency and duration of cluster periods and the frequency of the individual headache episodes increased over time. Cluster headache represent a treatable under-recognized cause of severe headaches in childhood and adolescence.