The purpose of this study was to evaluate the adequacy of the International Headache Society (IHS) criteria for chronic tension-type headache and, if appropriate, suggest modifications of the IHS classification. We evaluated 100 consecutive patients with chronic daily headache. Approximately two-thirds of our patients fulfilled the criteria for chronic tension-type headache. Most of the patients who failed to meet the criteria did so because they had more than one migrainous feature. Approximately 50% of patients took excessive amounts of analgesic medication. We conclude that the IHS criteria should be modified to include chronic daily headache evolving from migraine; subtypes with and without medication overuse should be distinguished.