The European Quality of Life-5 Dimensions (EQ-5D) questionnaire is widely used in oncology to generate quality of life weights (utilities). The typical purpose is to inform health economic evaluation studies. The EQ-5D is generally suitable for this purpose; it has shown a reasonable degree of reliability, content validity, construct validity and responsiveness in the majority of the available studies. In situations of doubt, combination with other quality-of-life instruments may be an option. The authors expect that the five-level version of the EQ-5D will gradually replace the three-level version, due to reduced ceiling effects and more appropriate responsiveness. Further research should address the benefits achievable through additional dimensions or patient-based valuation, and the validity of EQ-5D versions for proxy respondents.