OBJECTIVES: It is unknown whether minimal important differences (MID) identified on generic patient reported outcomes are consistent across disease states. This research compares mapped utility instrument MID values within four newly identified patient groups. METHODS: Retrospective analysis of a two-year longitudinal study in a Western US managed care population was conducted. Individuals receiving a prescription for a new disease state in either year were selected. Four major disease states, each with more than 100 patients reporting a minimal change in health over the past year on the SF-36 general health question were included. MID values were calculated for gains and losses in health on the Brazier, Lundberg, Nichol, and Shmueli mapped utility instruments. MID values between disease groups for each instrument were tested with ANOVA. Effect sizes were compared in accordance to Norman (2001) as a distribution-based method to determine the MID. RESULTS: Results are displayed for Brazier's SF-6D measure as all mapped utility instruments had similar results. 145, 240, 306, and 150 patients reported a minimal gain or loss in health over the year when they filled a new prescription for cardiac disease, COPD, depression and rheumatoid arthritis, respectively. The reported mean MID utility change for gains was 0.026, 0.022, 0.019, and 0.018 for each patient group, respectively (P=0.975). The reported mean MID utility change for losses was -0.069, -0.045, -0.055, and -0.028 for each patient group, respectively (P=0.217). The average effect sizes ranged from 0.133 and 0.194 for gains and from -0.241 and -0.627 for losses. Therefore, according to Cohen's classification system, the MID values in gains were not significant changes, while those in losses were considered small. CONCLUSION: This data demonstrates consistent, but small, MID values across various disease groups for each utility instrument. Researchers should confirm results in other populations.