OBJECTIVE: Health economists developed QALYs in the 1970s as an outcome measure combining duration and quality of life, primarily for use in cost-effectiveness studies. The concept of the DALY, as developed for the Global Burden of Disease (GBD) 1990 study, closely resembled the QALY. We identified the analogies and disparities of QALYs and DALYs from the literature and our own empirical experience with both approaches (EQ-5D, Dutch Disability Weights study). METHODS: The DALY is a gap measure, defining health loss from some predefined standard, whereas QALYs quantify health gains. The general approach to derive QALY values includes empirical valuation of generic health state descriptions, preferably using time trade-off, by a representative sample from the general public. For the GBD-1990, disability weights (DWs) were derived for disease-specific health state descriptions from an expert panel using person trade-off. QALY values and DWs, respectively, are combined with life-years directly and may be discounted, whereas DALYs additionally included age weights. RESULTS: We argue that, though apparent, the various valuation methods and respondent panels are not the most important differences. The important novelty of DALYs lies in the derivation of disease specific disability weights. Disease labeling adds information to an otherwise generic health state description and may have added to the validity of the weights, but also disclosed critical problems with the assumed utility independence of survival and quality of life. The standard QALY approach of summing separately valued one-year periods appeared not to work for diseases characterized by rapid transitions through different health states. CONCLUSION: The problems with DALYs uncovered some important limitations of the standard QALY approach. This may have important methodological implications for the evaluation of the effects of interventions for attack-type and short duration diseases.