In 2011, a new prospective payment system will be instituted for Medicare payments for dialysis.  CMS analyses revealed that dialysis payments differ significantly by race, yet CMS has not proposed including a racial case mix adjuster (CMA).  Initial analyses showed that the proposed payment system without a racial CMA produced significant underpayment in dialysis units serving large numbers of black patients.  OBJECTIVES: Model the impact of adding a racial case mix adjuster on dialysis reimbursement to clinics serving black patients, including a geospatial mapping to understand regional impact. METHODS: We used the racial case mix weights reported by CMS (though not included as a CMA), as well as the projected payments under the current and proposed payment systems.  We used updated census data on race on the county level for a national analysis, and actual race for analysis of only DaVita clinics.    We calculated clinic-level change in reimbursement using race CMA weights, then lowered the base payment rate to offset the incremental costs associated with the race CMA.  We then use geomapping to plot percentage change due to race CMA, and overall change in proposed payment, and differential between current payment and proposed payment with and without the racial CMA. RESULTS: Among the 4276 dialysis clinics analyzed, the addition of the race CMA increased payment in 1140 clinics and decreased payments in 1206 clinics; it increased payment by ≥2% in 292 clinics and decreased payment by ≥2% in 172 clinics.  Without the race CMA, payment reductions of ≥ 10% were disproportionately seen in areas in the southeast and in large cities with high percentages of blacks.  This was ameliorated by the addition of the race case mix adjuster. CONCLUSIONS: CMS should include a race CMA in the prospective payment system for dialysis.