OBJECTIVE: As the second most common primary headache, it follows that migraine is associated with substantial clinical and economic consequences. Migraine particularly impacts the labor force as its disabling effects frequently persist beyond the acute onset of an attack. With such effects in the work place, further understanding of the losses in productivity as a result of migraine is necessary. The objective of this study was to determine the indirect costs due to migraine in the U.S. population. METHODS: Retrospective analysis was conducted of the 1999 portion of the Medical Expenditure Panel Survey (MEPS). The MEPS provided data from a nationally representative sample of 24,618 respondents and data from respondents' medical care and health insurance providers and employers. Data utilized in this study included medical conditions and employment information comprised of hourly earnings, hours worked, and disability days. Migraine patients who incurred disability days were identified using International Classification of Diseases (ICD-9-CM) codes and variables denoting disability days. Indirect costs were calculated for migraineurs who missed workdays using the human capital approach. Sample estimates were weighted and projected to the population and 95% confidence limits for estimates were calculated using the Taylor expansion method. RESULTS: Total indirect costs of migraine patients who missed workdays were $3,895,041,461, with mean indirect costs of $2,273 per patient (95% C.L. = $1,665 to $2,882). Relative to the entire population, mean indirect costs per person were $14. CONCLUSIONS: With total indirect costs approaching $4 billion and per patient indirect costs greater than $2000, migraine continues to have a considerable impact on the work force. Additional steps should be undertaken to further develop diagnostic and treatment paradigms in an effort to reduce migraine-related absenteeism and lost productivity.