A history of previous primary cancer and of radiotherapy were investigated as risk factors for lung cancer in lifetime nonsmokers in a hospital-based case-control study. By design, subjects with a previous tobacco-related primary (of the lung, larynx, oropharynx, esophagus, kidney, bladder, or pancreas) were excluded. Information was available on 30 male and 47 female lung cancer cases and 87 male and 132 female controls, all lifetime nonsmokers, interviewed in hospitals in four United States cities between 1985 and 1990. In males, neither a history of a previous primary nor a history of radiotherapy was associated significantly with lung cancer; however, the numbers of exposed cases were small. In females, after adjustment for age, education, hospital, lifetime environmental tobacco-smoke exposure, and body mass index, both a history of a reproductive primary and a history of radiotherapy were associated significantly with lung cancer (odds ratio [OR] = 4.9, 95 percent confidence interval [CI] = 1.4-17.7, and OR = 4.4, CI = 1.3-15.1, respectively). Due to a high correlation between a history of a reproductive primary and a history of radiotherapy in the cases, it was not possible to estimate the effect of one exposure independent of the other. These results are consistent with the possibility that endocrine factors may play a role in some lung cancers in women.