Using questionnaire data from two recent surveys, headache sufferers were classified as having either migraine, episodic, or chronic tension-type headache using the International Headache Society criteria. Of 410 subjects with a headache history of 2 years or more, 147 or 35.9% were assigned Code 1.7 (migrainous disorder not fulfilling the above criteria) or Code 2.3 (headache of the tension-type not fulfilling above criteria). In 79 of these 147 subjects (53.7%), either of the above codes would have been equally valid. Separate scores for "migraine" and "tension" symptoms may provide a way to handle this overlap and aid in choosing optimal therapy.