The incidence of sciatic pain among 25–49 year-old men in three differnt types of work: machine operating, dynamic physical work (construction carpenters), and office work was assessed prospectively. Postal questionnaires both at the beginning and the end of the 3-year follow-up were answered by 1149 men who at baseline had no history of sciatic pain. The crude risk ratio of the incidence of sciatic pain was 1.6 (95% confidence interval 1.2–2.2) for the machine operators and 1.7 (1.3–2.4) for the carpenters when the office workers were referents. The adjusted risk ratios were 1.4 (1.0–1.9) and 1.5 (1.1–2.1), respectively. Previous history of severe lumbago or other low-back pain increased the risk fourfold. Frequent physical exercise and smoking were of borderline significance as predictors.