When valuing health states, health economists often ask respondents how many years of life in poor health they would be willing to trade off in order to live in full health. There are many problems inherent in eliciting preferences of this kind that have led us to advocate more direct measures of experienced utility. Yet individuals are often willing to make large sacrifices in life expectancy to alleviate conditions for which there is a considerable degree of hedonic adaptation. The purpose of this study is to investigate this important discrepancy in more detail. Data from 1173 internet and telephone surveys in the United States suggest that frequent and negative thoughts about health are significant in explaining time trade-off responses. We discuss some of the implications of these results for the measurement and valuation of health.