The main purpose of the present study was to define and understand more clearly the headache, and in particular the long-lasting attacks or continuous pain associated with the Chiari type I malformation. Of 34 patients with the malformation, the 20 patients who had or had had headache problems were interviewed according to a standardized questionnaire. Many patients had several headache types. Ten patients had shortlasting "cough headache" attacks lasting less than 5 minutes, 14 patients had relatively long-lasting attacks lasting from 3 hours to several days, and 8 patients had continuous headache. Unlike the short-lasting cough headache attacks, long-lasting attacks were usually not precipitated by Valsalva-like maneuvers. With discriminant analysis, this headache could rather well be differentiated from that of migraine and cervicogenic headache patients. In many respects, however, this headache resembled cervicogenic headache with occipital and neck pain, pain in the arm, restriction of neck movement, and dizziness often accompanying the headache. Dizziness was the most distinguishing feature in the Chiari patients. These features, together with a beneficial effect of surgical treatment in some patients, suggest a causal relationship between the malformation and headache. From the histories of a few illustrative cases, it is suggested that the malformation may cause long-lasting headache attacks or continuous head pain by compression of the brainstem, central cord degeneration or intracranial hypertension.