In a hospital-based case-control study, 391 male cases of primary lung cancer and the same number of controls—matched by sex, age, and region—were personally interviewed for their job and smoking histories. The data reported reflect the midpoint of a study aiming at a total of 1,000 cases. One objective of the study was to assess confounding by asbestos exposure in what was thought to be a welding-associated risk. While the odds ratios (OR) increased steeply with cumulative exposure to tobacco smoke and were raised also for lifelong asbestos exposure of over 4,100 working hours (OR = 1.91), the effect of welding exposure was reduced after adjustment for smoking and exposure to asbestos. Furthermore, no consistent dose-response relationship could be shown in relation to welding hours. Therefore the present study supports the hypothesis that some, if not all, of the excess risk of welders observed in the literature may be due to the exposure to asbestos. The finding that the subgroup of employees in the aircraft industry showed an increased odds ratio of 2.14 after adjustment for smoking and exposure to asbestos deserves further attention. This suggests the need for further research on the role of berryllium-containing alloys, which has been suggested by other authors.