This paper considers the question of what ought to be valued in the context of measuring the outcomes of healthcare interventions. The answer is discrete health states in the case of the quality-adjusted life-year (QALY) model and an entire health profile in the case of the healthy-years equivalent (HYE) approach. How well the weighted average of values attached to the former approximates the overall value attached to the latter depends on the validity of the assumptions of the QALY model. The paper considers some of the empirical literature relating to them. One of the most important assumptions, which from the limited evidence available appears not to hold, is additive separability. However, it is argued that violation of this assumption does not in itself invalidate the QALY approach, since in some circumstances it might be more appropriate to elicit the value of a health state independently of the states that succeed it. Investigation into this issue is identified as one of the key areas where future research efforts should be directed.