Valid data on the occurrence of lung cancer among nonsmokers are sparse and refer mainly to North American populations. The objective of our study is to provide an estimate of the incidence of lung cancer among non-smokers in a large European population. Proceeding from a nationwide health care program among Swedish construction workers, we estimated the incidence of lung cancer among 143,998 males who reported to be never smokers at 1 or several physical check-ups (average, 2.9 visits) during 1971-92. Cancer incidence data for 1971-95 were obtained through linkage with the virtually complete national cancer registry. Cohort members contributed over 2 million personyears of observation, during which 101 lung cancers occurred. The age-standardized rate was 3.7/100,000 (95% confidence interval [CI] 2.8 -4.6). There was a suggestion of a calendar period effect, with rates increasing from 1.5/100,000 in 1976 -80 to 5.4/100,000 in 1991-95. A birth cohort effect was also suggested. Rates estimated in this population are comparable to those from North American studies. The increasing rate during the study period might be due to non-smokers who took up the habit, but it might also reflect temporal changes in the effect of other risk factors of lung cancer in non-smokers.