In order to estimate the proportion of bladder cancers attributable to occupation in different countries, three criteria were defined, each with a different degree of strictness, for the inclusion of job titles or industrial activities in the estimates. Such criteria were applied to the available case-referent studies, the range for the less severe criterion estimates being 0-19% and that of the strictest being 1-19%. The variability was greater among the studies than among the criteria of inclusion of occupations; therefore the study design and time- and place-specificity of exposures play an important role in the magnitude of such estimates.