Abstract : Headache is an important individual and societal burden. Despite an important prevalence, migraine remains an underdiagnosed and undertreated disease. Large population-based epidemiological studies are available in many countries, but not in Belgium. We decided to assess 1 year prevalence and loss of productivity due to headaches in a sample of workers representative of the active Belgian population, the employees and workers of Liège University (ULg). A structured questionnaire based on the diagnostic criteria of the International Headache Society (IHS) was sent to the 1467 members of the ULg personnel in 2002. Among them, 212 (14.5%) had suffered of at least one headache in the previous 12 months ; 163 (77%) fulfilled the criteria for migraine, 49 (23%) had other headache types. One year-prevalence was 13% for migraine, 3.9% for other headaches. Among migraineurs there were 83% females, 19% had migraine with aura and the majority (49%) had 1-2 attacks per month. Acute anti-migraine treatment was taken by 98% of migraineurs, among whom only 9% used triptans. Intake of acute treatment more than twice per week, which tends to chronify headaches, was mentioned by 29% of migraineurs. Although 35% of subjets reported more than 2 attacks per month, only 13% were taking preventive anti-migraine treatment. The correct diagnosis of migraine was known to 51% of migraineurs, while 28% of non-migraineurs thought they were suffering from migraine. During the 3 months preceding the survey, 60% of migraineurs had to reduce (48%) or totally interrupt work (12%) at ULg for at least 1 day. Taking into account the mean salary at the ULg, the cost due to lost productivity was estimated at 300,000 € per year. This cost could be more than halved by an adequate anti-migraine treament.