The prevalence of low back syndrome and its consequences in terms of disability, handicap, and need for medical care were studied as part of "the Mini-Finland Health Survey". A sample of 8000 persons representative of the Finnish population aged 30 or over was invited for examination, and 7217 (90%) participated. At interview 75% of the participants reported that they had experienced at least one episode of low back pain. Six or more episodes were reported by half of the population, and about 20% had suffered from pain during the previous month. On the basis of a standardised clinical examination, a physician diagnosed low back syndrome in 17.5% of men and 16.3% of women. The prevalence was highest in those aged 55-64 years. The use of health services was frequent among those suffering from low back pain. Nevertheless, their need for care was commonly unmet. Some disability was found in almost 60% of the subjects with low back pain, although severe functional limitations were rare. It was estimated that of the work disability the reduced capacity for everyday duties apart from work, and the reduced capacity for leisure time activities, in the population 18%, 16%, and 17%, respectively, were attributable to the low back syndrome. Thus low back syndrome has a strong impact on individuals and on society as a whole.