OBJECTIVES. This study sought to provide data on the relationship of work exposures to long-term back problems in a population survey. METHODS. The Ontario Health Survey in 1990 used a representative population sample of the province. It included data on long-term back problems, occupational activity, and physical work exposures. The current study examined relationships between these variables. RESULTS. The prevalence of long-term back problems was 7.8% in working-age adults. It generally increased with age. Long-term back problems were more prevalent in blue-collar occupations and among those not working, as well as among people with less formal education, smokers, and those overweight. Physical work exposures--awkward working position, working with vibrating vehicles or equipment, and bending and lifting--were all associated with a greater risk of back problems. The number of simultaneous physical exposures was monotonically related to increased risk. CONCLUSIONS. Within the limitations of the data and assuming the relationship to be causal, about one quarter of the excess back pain morbidity in the working population could be explained by physical work exposures.