Background. Although the effects of cigarette smoking on cancer risk have been well documented, there remain several outstanding issues to be clarified, including the etermination of which types of cancer are associated with smoking and estimation of the magnitude of the effect of smoking on different types of cancer. A further Issue is whether the effects seen elsewhere can be demonstrated in Canada, where tobacco products differ somewhat from those in other countries. Methods. A case-control study was undertaken In Montreal to investigate the associations between a large number of environmental and occupational exposures on the one hand, and several types of cancer on the other. Between 1979 and 1985, interviews were carried out with incident male cases of 21 types of cancer, including 15 anatomical sites and six histological subtypes. The interview was designed to obtain detailed information on smoking histories, job histories, and other potential confounders. Altogether, 3730 cancer patients and 533 population controls were Interviewed. For each type of cancer analysed, two control groups were used: population controls and cancer controls (selected from among other cancer patients). The purpose of the present analysis is to estimate the relative risk of each of 21 types of cancer In relation to smoking and to estimate the percentage of cancer cases attributable to cigarette smoking. Results. Separate analyses conducted with the two control groups produced similar results. Of the many sites of cancer examined, the following were not associated with cigarette smoking: colon, rectum, liver, prostate, kidney and skin (melanoma). Within the lymphoreticular system, there was no excess risk of Hodgkin's lymphoma, although the results for non-Hodgkin's lymphoma were weakly suggestive of an association with smoking. The following sites were dearly associated with smoking: lung (odds ratio [OR] = 12.1), bladder (OR = 2.4), oesophagus (OR = 2.4), stomach (OR = 1.7), and pancreas (OR = 1.6). Population attributable risk percentages due to smoking were 90% for lung, 53% for bladder, 54% for oesophagus, 35% for stomach, and 33% for pancreas. Conclusions. Of the 21 types of cancer examined, the following were associated with smoking among men in Montreal: lung (induding all major histological subtypes), bladder (and its main histological subtypes), oesophagus, stomach and pancreas. Smoking likely accounts for a large proportion of cancers occurring at these sites.