OBJECTIVES: We converted disease specific outcomes of treatment for erectile dysfunction (ED) using sildenafil (Viagra) into Quality Adjusted Life Years (QALYs). Due to size and complexity of most disease specific questionnaires, application of this (recommended) strategy is scarce and detailed reports about valuation exercises of disease specific health states are lacking. Such valuation studies are needed to adapt existing methods to this new strategy. METHODS: 200 subjects from the general public and 110 ED-patients valued 25 ED-states with Time Trade-Off to convert the outcomes of a clinical trial into utilities. The health states reflect different gradations of ED, as categorised by questions 3 and 4 of the International Index of Erectile Function (IIEF). Those questions were suitable for our purposes because they describe the primary endpoints of ED-treatment, as defined by the National Institutes of Health. To test content validity and feasibility of valuing ED-states, we explored the relation between the values and background variables and analysed the factor structure of the valuation space in patients and the general public. RESULTS: The factor structure of the valuation space was the same in patients and the general public and values were not influenced by background variables, supporting validity and feasibility of valuing disease specific outcomes. According to the general public the mean improvement on the IIEF equals an increase of utility from 0.76 to 0.87 on a scale of 0 (dead) to 1.0 (perfect health). CONCLUSIONS: Treatment preferences can be measured by attaching utility weights to disease specific outcomes. The implication is that in cost-effectiveness analysis results can be available quickly, even if only disease specific outcomes are available from previous research. On basis of the utility gain of 0.11, we expect the costs per QALY of sildenafil to be about US $ 10,000.