In a cross-sectional epidemiological survey of a general population, headache disorders were diagnosed according to a structured interview and a neurological examination using the criteria of the International Headache Society. The prevalences and sex distribution of the primary headache disorders were assessed, and characteristics of and interrelationships between different types of headache were analyzed. Severity and frequency of migraine attacks were not correlated, indicating that the migraine attack is an all-or-none phenomenon triggered with an individually variable threshold. Tension-type headache, in contrast, showed increasing severity with increasing frequency, indicating that it is a graded phenomenon. In the previous year, 6% had migraine without aura (previously called "common migraine") and 4% had migraine with aura (previously called "classic migraine"); 63% had episodic tension-type headache and 3% chronic tension-type headache. In women, migraine without aura was twice as prevalent as migraine with aura; in men, an opposite trend emerged. In migraine without aura, pain was more severe than in migraine with aura. Tension-type headache in migraineurs was not significantly more prevalent than in nonmigraineurs and, except for greater frequency and severity, it did not deviate nosographically from pure tension-type headache. Our results support the contention that migraine and tension-type headache are distinct entities, contradict the so-called continuum-severity model, and indicate that the terms combination headache, mixed headache, and interval headache should be avoided.