This study estimates the 1-year prevalence of migraine in adults in England in relation to the major demographic variables of age, gender and ethnicity, and describes some of its features, including aspects of consequential disability. A telephone survey was conducted of a random sample (n = 4007) of the population aged 16-65 years of mainland England using a previously validated diagnostic interview. The response rate was 76.5%. Overall, 7.6% of males and 18.3% of females reported migraine with or without aura within the last year meeting diagnostic criteria closely approximate to those of the International Headache Society. Prevalence of migraine varied with age, rising through early adult life and declining in the late 40s and early 50s. Prevalence was higher in Caucasians than in other races. Attack rates were > or = 1/month in most migraineurs, and most experienced interference with daily activities in > or = 50% of their attacks. On average, an estimated 5.7 working days were lost per year for every working or student migraineur, although the most disabled 10% accounted for 85% of the total. Results were in keeping with those from surveys in other countries. If these findings in mainland England are projected to the entire UK population, we estimate that 5.85 million people aged 16-65 years experience 190 000 migraine attacks every day and lose 25 million days from work or school each year because of them. Migraine is an important public health problem in the UK, associated with very substantial costs.