Because the causal relationship between tobacco smoking and lung cancer has been clearly established, we have set out to measure its magnitude among the Spanish population in the time period 1940-1988 using observational methods. To do so, we have carried a time series study of ecological data. Information on lung cancer mortality, tobacco smoking and other potential predictors of lung cancer has been elaborated from official statistics. Data analysis has been performed by graphical methods and multiple linear regression techniques. Lung cancer mortality, tobacco smoking, total lipid intake and the Spanish wealth, as measured by national per caput income and gross domestic product, have increased very importantly over the study period. After controlling for the effect of lipids and alcohol intake, for every gram/per caput/day of increase in tobacco smoking in the period 1940-1988, there has been a 19% increase in lung cancer mortality with a 15 year lag. We conclude that tobacco smoking has fueled the lung cancer epidemic in Spain during the study period. This finding provides additional arguments for the implementation of tobacco control programmes in our country.