Abstract. This article is intended to systematicaly show all the conditions that the Quality Adjusted Life Year (QALY) must satisfy so that it can be interpreted as a von Newman-Morgenstern utility. Such conditions cover two cases. When health states are chronic, we shall be referring to the conditions inferred by Pliskin, Shepard and Weinstein (1980). Likewise, we will devote our attention to commenting on the characterization of Bleichrodt (1996), pointing out that its condition 0 is a bit artificial. In turn, for temporary health states, we will remark that the characterization of Bleichrodt (1995) appears to be incomplete. We shall provide a complete derivation of QALYs. In this way, QALYs can be derived from an individual's preference relation that satisfies the von Newman-Morgenstern axioms by imposing additive independence, absence of contradictory trade-offs and partial symmetry. Moreover, the two last conditions conditions can be replaced by a single condition that we call general symmetry.