It is meaningless to discuss the prevalence of TTH if the frequency of attacks is not considered. TTH once or twice a year is a nuisance, whereas CTTH is clearly a disease with a major impact on the individual. In the Danish epidemiologic studies the majority of the general population (51% to 59%) had infrequent TTH one day per month or less and did not require specific medical attention. These TTH subjects cannot be regarded as patients (29,30,37). However, in most studies 18% to 37% had TTH more than once a month, 10% to 25% had TTH weekly, and 2% to 6% of the population had chronic TTH usually lasting for the greater part of a lifetime (Table 67-1) (15,18,22,29,42, 46,47,49). Global prevalence of CTTH is quite uniform at 2% to 3% (Table 67-1) (11,15,18,24,26,29,42,46,47,49). In Chile, TTH represents 72.3% of all headaches (26).

The prevalence of TTH is much higher in two Danish population studies (29,36) than in most other population studies (11,15,18,42,46,47,49), where the prevalence estimates generally vary between 16% and 39%. There may be several, mostly methodologic, explanations for this. The diagnoses of frequent and infrequent ETTH that were introduced in IHCD-II (20) improve comparison between studies. Most investigators have asked, “Do you suffer from tension-type headache?” and may thereby have excluded subjects with infrequent or mild TTH. The Danish study aimed to include all regardless of frequency and severity and asked, “Have you ever had a tension-type headache?” (36,39). After exclusion of subjects with infrequent TTH, the prevalence of frequent ETTH and CTTH show consistent prevalence in different studies (Table 67-1). A recent population study of adults reported an increase in frequent ETTH and CTTH (29). A similar increase has been reported in Sweden (25).

In the selected population studies where TTH has been reported, the prevalence is also rather uniform. In Brazilian medical students the prevalence of frequent ETTH was 32.1% (12), in a Dutch manufacturing setting it was 34.5% (35), and in medical students from Kenya it was as much as 50% (2).

Daily or near daily headaches are a major diagnostic and therapeutic problem in specialized headache clinics and account for 40 to 50% of the patients (8,10,23,34,45), although the prevalence in the general population is between 4% and 5% (10,24,48). There is considerable debate regarding terminology. The terms daily headache or chronic daily headache have been widely used in the literature but are not internationally accepted or included in either version of the IHS classification (1,17,20,21). The vast majority of these patients with chronic daily headache may also have medication-overuse headache. Distinguishing CTTH from migraine and from medication-induced headache is a diagnostic challenge but is of importance as the management is completely different.