Fire fighters are exposed to irritating, asphyxiating, and toxic gases and aerosols, to psychological stress, and to physically demanding work. Due to differences in fire fighting techniques, exposure conditions for fire fighters differ among different countries. The purpose of this investigation was to study cancer incidence and mortality in fire fighters who have been working with fire fighting methods used in Sweden from the beginning of this century onwards. All male fire fighters employed for at least 1 year in the City of Stockholm during 1931-1983 were traced, and an index of the number of fires fought was calculated for each individual. The mortality during 1951-1986 (among 1, 116 fire fighters) was lower than expected (SMR = 82; 95% confidence interval 72-91) compared with local mortality rates, with a low mortality in circulatory diseases, obstructive lung diseases, violent deaths, and suicides. The cancer incidence in 1958-1986 was equal to the expected (SMR = 100; 95% confidence interval 83-119). However, an excess of stomach cancer (18 observed vs. 9.37 expected; SMR = 192, 95% CI 114-304) was observed. There was also a tendency for higher incidence and mortality in stomach and brain cancer with increasing number of fires. There were four deaths from brain cancer compared to 0.8 expected (SMR = 496; 95% CI 135-1270) in the highest exposure category. Fire fighters are, however, not systematically exposed to known stomach or brain carcinogens, and the results need confirmation in further studies with extensive exposure evaluations.