The objectives of the study were to estimate the rate of 1-year incidence of occupational back pain, describe the duration of absence from work, and assess medical and economic aspects of this problem. A total of 2,523 files of occupational back pain, representative of the Province of Quebec for the year 1981, were examined by a multidisciplinary team. Census data from 1981 were used for the denominators. The overall 1-year incidence in 1981 was 1.37%. The age-specific incidence rates show an increase-decrease pattern that could be interpreted as a "healthy worker effect". The male to female relative risks by age range from 5.6 (20 to 24 years old) to 1.8 (55 to 64 years old). In the 1-year follow-up, 74% of the workers were absent for less than 1 month. The 7.4% of cases who were absent from work for more than 6 months accounted for nearly 75% of lost days, medical costs, and indemnity payments. We pinpoint some methodologic issues of studies on occupational back pain.