The disability-adjusted life year (DALY) measure combines nonfatal outcomes and mortality in a single summary measure of population health. One DALY represents 1 lost year of healthy life. The basic philosophy associated with the estimation of DALYs is (a) use the best available data, (b) make corrections for major known biases in available measurements to improve cross-population comparability, and (c) use internal consistency as a tool to improve the validity of epidemiological assessments. For the latter purpose, a software application, DISMOD II, is available from the World Health Organization (WHO) Web site.