A cluster headache is an attack of half-sided very strong pain in or behind an eye, lasting for up to a few hours with tearing and rhinorrhea and sometimes Horner's syndrome. The attacks occur in clusters of weeks' to some months' duration. A cluster headache is a neurovascular primary headache which seems to involve the hypothalamus. The clinical picture, diagnosis and investigations are reviewed. The attack can be treated with oxygen or subcutaneous sumatriptan, and verapamil, ergotamine and prednisolone can be successfully used for prophylaxis. Early diagnosis and specific treatment are emphazised.