A case-referent study was carried out to investigate the relationship between lung cancer and exposure to silica dust in an area where a relatively high proportion of the workforce was exposed to silica dust in the past. The cases were 309 lung cancer patients admitted at the Chest Department of the Central Belluno Hospital during the period 1973-1980, while the 309 controls were patients admitted at the same department for diseases other than lung cancer and bronchitis during the same period. Information on exposure to silica and smoking habits were collected from hospital records. The results show an elevated risk, supported by a clear dose-response, due to smoking. Exposure to silica also appears to increase the risk of lung cancer, but only in presence of silicosis. The risk estimates tend to increase both with amount of smoking and duration of exposure to silica, with the magnitude of the risk being, however, much smaller for the latter effect. No clear interaction appears to exist between the two factors. The limitations of the study and the problems in interpreting the results are discussed.