A new instrument, the Diagnostic Headache Diary, based on the operational diagnostic criteria of the International Headache Society (IHS), was tested in 61 migraine patients from a headache research clinic using the clinical diagnosis (IHS criteria) for comparison. All patients kept the diary for one to eight months. The clinical and diary diagnosis of migraine with and without aura was the same in, respectively, 72 and 87% of the patients. Nausea, photophobia and phonophobia tended to be more pronounced at the clinical interview. The diary identified 20 more cases of episodic tension-type headache and 15 fewer cases of chronic tension-type headache than the clinical interview. Two blinded observers always made the same IHS diagnoses when interpreting the diagnostic headache diary. A combination of a clinical interview and the diagnostic headache diary gives a qualitatively and quantitatively more precise diagnosis than a clinical interview alone.