OBJECTIVE: Quality-adjusted life years (QALYs), which rely on preference-based measures of health, are widely used as outcome measures in cost-effectiveness studies. However, for Overactive Bladder (OAB), none of the existing disease-specific measures are preference-based, whereas existing generic preference-based measures of health have been shown to be insensitive in OAB patients. The purpose of this study is to estimate a preference-based single index using the validated Overactive Bladder Questionnaire (OAB-q). METHODS: Psychometric criteria were used to select a subset of the 33 OAB-q items to form a new classification amenable to valuation. This reduced system has 5 dimensions; each with 5 rating levels ranging from no problems to extreme problems. An interview valuation survey of members of public in the South Yorkshire was undertaken using the time trade off (TTO) method. Each respondent was randomly allocated to one of 14 blocks, and valued 7 states each, so that a total of 98 states were valued. A number of multivariate regression models were estimated for predicting total 3125 health states values defined by the reduced classification. Models were compared and selected based on prediction ability and consistency of coefficients. RESULTS: Three hundred and eleven members of general public were interviewed with 51.4% female and mean age 42. 42.6% have some OAB symptoms. These respondents produced a total of 2487 health state values. Mean health state values range from 0.56 to 1.00, with standard deviations from 0.2 to 0.3. The mean no-constant model was chosen as the best model. Mean absolute error (MAE) of the best model was 0.044, with results for the EQ-5D of 0.039. CONCLUSIONS: This paper presents a method for deriving QALYs using existing and future OABq data sets. This will permit the cost effectiveness of new interventions to be assessed in patients with OAB.