The frequency of sciatic pain, lumbago, and nonspecific low-back pain (LBP) and factors related to these symptoms were determined among men occupied in machine operating (541 longshoremen and 311 earthmover operators), dynamic physical work (696 carpenters), and sedentary work (674 municipal office workers). Sciatic pain was more common among machine operators and carpenters than among office workers, and also more frequent among machine operators than among carpenters. The occupational differences were considerably smaller with regard to lumbago and nonspecific LBP. In multivariate analysis, occupation, age, reported back accidents, and postural load showed significant independent effects on the occurrence of sciatic pain. Allowing for other risk indicators, the relative risk was 1.3 contrasting machine operators with both office workers and carpenters, but carpenters had no excess risk as compared with office workers.