Eighty-one patients were diagnosed as having migraine, tension headache or both according to previously used criteria. Then we performed a standardized interview to determine the frequency and severity of headache characteristics used in the new operational diagnostic criteria of the International Headache Society (IHS). In every patient the original diagnosis fulfilled also the IHS criteria, but in 9 patients the criteria were only fulfilled in half or less of the attacks, and applying the IHS criteria they also achieved an additional diagnosis. In one patient these attacks did not fulfill the pain criteria and in 8 (4 migraine, 4 tension headache) they did not fulfill the criteria for accompanying symptoms. Overall the IHS criteria are sensitive and specific, but they may possibly be improved with regard to accompanying symptoms. The present study suggests that recording of frequency and graded severity of characteristics using a headache diary may further improve the distinction between the different types of headache.