This study examines sex differences in the relative risks of lung cancer and other smoking-related cancers (i.e. cancers of the upper respiratory tract, oesophagus, pancreas, bladder, and renal pelvis). Data on smoking habits in 1963 from a random sample of 56,000 men and women were linked with information on new cases of cancer for 1964-89. Compared with people who have never smoked, the relative risks of lung cancer at different levels of pack-years completed in 1963 (>5, 6-15, 16-25 and 25 + pack-years) were 1.6, 4.4, 14.2, and 17.9 for men, and 2.1, 6.3, 10.3, and 16.5 for women. The corresponding relative risks of other smoking-related cancers were 1.8, 3.0 5.4, and 6.4 for men, and 2.0, 3.1, 5.0, and 6.5 for women. These results suggest that men and women have similar relative risks of smoking-related cancers at different levels of smoking.