The aim of this large, cross-sectional, population-based study was to examine the association between sick leave and headache. Between 1995 and 1997, all 92 566 adults in Nord-Trøndelag County in Norway were invited to participate in a health survey. Out of 73 327 invited individuals <67 years old, a total of 38 192 (52%) responded to questions about headache, work situation and sick leave during the past year. Associations between sick leave, headache and migraine included were assessed in multivariate analyses, estimating prevalence odds ratios (ORs) with 95% confidence intervals (CIs). There was an increasing prevalence of sick leave with increasing frequency of migraine and non-migrainous headache. The prevalence of sick leave >8 weeks during the past year was more than three times higher among individuals with headache >14 days per month (20%) compared with those without headache (6%). The results may indicate that better treatment of individuals with chronic headache may have beneficial economic implications.