Headache is a common symptom in primary care about which surprisingly little is known. Over a 14-month period 3847 patients making 4940 consecutive visits for headache to 38 primary care practices in the USA and Canada were studied. The clinical characteristics of patients, as well as the diagnostic and therapeutic strategies employed by their doctors, were examined. Visits for headache represented 1.5% of all visits during this period. Most patients (72.0%) made only one visit, and nearly half of the headaches reported were new. Only a small number of patients (3.0%) received a computerized tomographic scan; other investigations were used sparingly, as were referrals to consultants (5.0%) and hospitalizations (2.2%). Drugs (75.2%) and advice (64.5%) were commonly employed, although formal psychotherapy was recommended infrequently (4.5%). It is concluded from this large series that most patients with headache visit primary care practitioners only once; their headaches frequently defy usual diagnostic categorization and often change in character from visit to visit. Moreover, headaches in this series were frequently associated with a variety of causes not often included in discussions of headache aetiology. These findings suggest that the strategies which doctors in primary care devise to diagnose, investigate and manage this common symptom, require further study.