We tested the usefulness and applicability of a simplified headache diary in the diagnosis of migraine (M), tension-type headache (TTH) and medication overuse headache (MOH). The diary was given to headache patients before their first consultation at the headache centre. Seventy-six naive headache patients completed the study. Their understanding of the diary proved highly satisfactory. The patients' level of compliance was also good, with 71% returning the diary completely filled in. The data entered in the diary were deemed complete for the diagnostic purpose in 93% of cases. The level of agreement between headache information gathered through clinical interview and the headache diary was satisfactory. When comparing the diary with the clinical interview, sensitivity was 92% for M, 75% for TTH and MOH. Specificity was 58% for M and TTH, 87% for MOH. Combined use of a diagnostic diary and clinical interview is recommended from the first consultation for headache.