BACKGROUND Population-based surveys estimate the prevalence of chronic daily headache (CDH) in the general community to be approximately 4%. The prevalence of CDH among patients seen in the primary care setting in the United States, however, is unknown. OBJECTIVE To estimate the prevalence and associated burden of suffering of CDH in a primary care patient population. METHODS Cross-sectional survey of a randomly selected sample of 1500 adult patients in an academic Family Medicine Center was done. Outcome measures include self-reported headache frequency and Headache Impact Test scores. RESULTS Completed questionnaires were returned by 853 (57%) patients. The mean age of respondents was 49 years (SD = 16), with a range of 18 to 94 years. Two hundred ninety-six (58%) patients reported having had 1 or more severe headaches in the past month. Seventy-four (9%) patients reported a frequency of headache consistent with CDH, defined as the occurrence of headache 15 or more days in the past month. Twenty-four patients (32%) with CDH either believed that none of their doctors know that they experienced headaches or were not sure if their doctors were aware of their headaches, and 21 (28%) reported that they have not needed a doctor's care for their headaches. CONCLUSIONS The prevalence of CDH is greater among a primary care patient population compared to the general community. A substantial proportion of patients with CDH do not bring their headaches to the attention of their health-care providers. In light of the advances in the development of effective medications for migraines and the growing body of evidence implicating medications as a contributing cause of CDH, it may be appropriate to encourage patients to inform their health-care providers about their headaches and to encourage providers to identify patients with frequent headaches.