One objective of the DSH allocation policy is to use an indirect measure of a hospital's costs of providing care to low-income patients. When discharges are used as an allocation statistic, differences in a hospital's case mix need to be taken into account. Since data on a hospital's overall case mix are not readily available, we examined measures that might be used as a proxy such as the Medicare case mix index. We found that there is only a moderate correlation between the Medicare case mix index and the Medicaid case mix index (0.504) and the case mix index for all low-income patients (0.624). An alternative to using a case mix would be to use the proportion of days or charges as the low-income patient measure.