BACKGROUND: Economic evaluations are used as a tool for making priorities in the health care sector and this tool should in principle, reflect individuals’ preferences. In economic theory, utility is seen as a way to describe preferences. The utility of life years gained in economic evaluations of health care programmes has commonly been treated as a linear function of life years gained even though some empirical evidence suggest a diminishing marginal utility for lifetime. A power function with a factor less than 1 in the quality-adjusted life-years (QALY) model has been suggested to account for risk aversion and positive time preferences.METHODS: In this study, the utility of gain in lifetime up to 1 year was examined in a random sample of 2,400 Norwegians aged 40 to 59 years old. In hypothetical scenarios, respondents with untreated remaining lifetime of 1 or 10 years were offered treatment with a life gain ranging from 1 week to 1 year. The utility of the treatment was measured as willingness-to-pay (WTP) in an individual perspective. RESULTS: The acceptance rates for offers of life extension treatments with a fixed price per week was increasing with longer life extensions and this indicates an increasing marginal utility for lifetime gains up to one year. However, the maximum WTP/week was decreasing with longer lifetime gains, which might be attributed to reduced ability to pay for longer gains. There was no clear lower threshold value for a gain in life extension to be considered worthwhile. CONCLUSION: If an increasing marginal utility for lifetime gains up to one year reflects the population’s preferences, the standard linear QALY model and the power QALY model proposed may yield misleading results for decision-making, and QALY weights obtained through TTO may be biased.