BACKGROUND: The EXACT (Exacerbations of COPD Tool) is a daily diary used in clinical trials to evaluate frequency, severity, and duration of COPD exacerbations. Reporting utilities from the EXACT allows a more accurate account of preference change for economic evaluations than current methods. Multi-attribute utility theory (MAUT) employs a series of equations to develop a function (MAUF) to report utilities. OBJECTIVES: To develop and validate an MAUF to estimate utilities from the EXACT for use in UK cost-effectiveness studies. METHODS: EXACT-U is comprised of 5 items with 3-5 levels each. Items and levels were grouped to form mixed-level and corner health states.  Development group was used for MAUF construction; separate Validation group was used to test functions. UK general public respondents valued 11 health states (including best/worst) using TTO from full health/dead over 10 years. MAUF used the multiplicative model by: (1)-Calculating mean utility of each attribute level; (2)- Calculating group disutilities for each level; (3)-Applying multiplicative model to derive disutility function; and (4)-Converting disutility function to utility function. Performance assessed by: number of inconsistencies predicted, mean absolute error (MAE), and root mean squared error (RMSE).  Models validated using a secondary analysis of a separate dataset of EXACT patient data to test discriminant validity (statistical significance) and responsiveness (standardized response mean (SRM)). RESULTS: TTO interviews conducted with 400 respondents: 350 Development group, 50 Validation group. Respondents were: 36 yrs old (13.5 SD), 39.2% male, and 46.4% White British.  MAUF reported MAE=0.032, and RMSE=0.170. Discriminant validity supported by utility differences by clinical severity: stable/acute (p=0.001); mild/moderate (p=0.01); moderate/severe (p=0.0001); and severe/very severe (p=0.14). Responsiveness by SRM was 0.52 (Day 3), 0.55 (Day 7), 0.66 (Day 10), and 0.76 (Day 13). CONCLUSIONS: The EXACT-U is a condition-specific preference-based measure to report COPD exacerbation utilities with minimal error, good discrimination, and good responsiveness.