Aims: We tested the usability and usefulness of the basic diagnostic headache diary (BDHD) for the diagnosis of migraine, tension-type headache and medication-overuse headache in European and Latin American countries. Methods: Patients were subdivided into two groups according to a 1:1 randomization list. Those in group 1 were sent the BDHD before their first visit to the headache centre and asked to complete it for at least 1 month. Those in group 2 made their first visit to the headache centre without receiving the BDHD. Results: A total of 626 patients from nine countries and 16 centres completed the study. The BDHD entries were complete in 97.5% of cases. BDHD information and clinical interview were, when taken together, considered complete for diagnosis in 97.7% of cases in group 1 whereas the information obtained by clinical interview alone in group 2 was considered complete in only 86.8% of cases (p¿