The level of agreement between headache information, attained by clinical interview and headache diary, was evaluated in subjects who frequently suffered from headache and were participating in an epidemiological study of headache. One hundred and six subjects were interviewed and asked to complete a diary for a period of 4-8 weeks; 46% completed the study. For migraine the diary and clinical diagnoses demonstrated agreement in 82%, kappa value 0.57, sensitivity 90% and specificity 64%. For tension-type headache they demonstrated agreement in 87%, kappa value 0.39, sensitivity 97%, specificity 29% and a good agreement of frequency of tension-type headache was also obtained. In migraine, but not in tension-type headache, accompanying symptoms tended to be overestimated in the interview. The diary was not useful for the diagnosis of migraine with aura, but proved valuable in distinguishing between migraine and tension-type headache, and in the identification of coexisting headache disorders. Combined use of a diagnostic diary and clinical interview is recommended.