There are a number of measures that quantify the public health burden due to specific risk factors for specific diseases. Although these measures are of importance for policymakers, epidemiologists do not often calculate them or may be unfamiliar with some of the issues involved when they do. The primary measure of interest is the attributable fraction (AF), representing the fraction of cases or deaths from a specific disease that would not have occurred in the absence of exposure to a specific risk factor either in the exposed population or the population as a whole. AFs can be multiplied by the total number of cases of a given disease to obtain a "body count"--the absolute number of preventable cases due to a specific risk factor. Two other measures of public health burden, used in conjunction with AFs, are attributable years-of-life-lost and attributable disability-adjusted life-years. We provide an overview of the AF and related measures and discuss some of the specific issues involved in calculating AFs. These issues include calculating the variance of AFs (such as Monte Carlo sensitivity methods), biases arising from some formulas for the AF, sources of data for calculating AFs, dependence of AFs on basic decisions about what exposure-disease associations are causal, and extrapolation from the source population to the target population.