The Medicare program reimburses dialysis providers a flat rate for a bundle of services that comprise the basic dialysis treatment. This payment system is being modified to incorporate case-mix adjustment for age and body size, which have been shown to influence dialysis costs. This study simulated the economic impact of the recently issued Medicare rule on case-mix adjustment by estimating the variation in payments across patients, facilities, and broad classes of facilities. Case-mix adjustment results in considerable patient-level variation in payments (dollar 12.99 SD in case-mix adjusted payments). The variation across dialysis facilities is smaller but still economically significant (dollar 3.77 SD). However, there was little evidence that particular classes of facilities (e.g., ownership, chain membership, size) will be substantially advantaged or disadvantaged by case-mix adjustment. There do seem to be modest changes in the regional distribution of payments.