[en] Alpha track radon detectors were placed in the homes of 35 lung cancer patients and 35 matched controls for a period of 8 to 10 mo. Twenty lung cancer patients had small cell lung carcinoma; 11 had adenocarcinoma, 2 had squamous cell carcinoma, and 2 had unclassified carcinoma among 15 nonsmokers. Mean overall living on ground level was significantly higher in the group with small cell lung carcinoma (50 y ± 15) than among controls (33 y ± 19); the adjusted odds ratio for lung cancer was 5.2 (90% confidence interval [90% CI] = 1.1--24.9) per decade of living on the ground floor for the group with small cell lung carcinoma. Radon exposure of more than 1.0 pci/l in the group with small cell lung carcinoma was associated with increased risk of lung cancer, although it did not reach statistical significance [odds ratio = 1.5 (90% CI = 0.4--5.4)], adjusting for differences in smoking habits. The study supports the presence of a differentially increased risk for small cell lung carcinoma following long-term radon exposure. 12 refs., 2 tabs