A recent validation analysis at our center among allogeneic hematopoietic cell transplant (HCT) recipients did not find the HCT-specific comorbidity index (HCT-CI) to clearly segregate patient's transplant-related risk. We hypothesized that the discriminating and predictive power of the HCT-CI for mortality could be improved by eliminating the assignment of categorical weights to comorbidities and instead replacing them with hazard ratios (HR) from a Fine and Gray adjusted regression model. This approach allowed us to look carefully at each component of the comorbidity index. We developed the modified comorbidity index (MCI) using a cohort of 444 adult allogeneic HCT recipients using a pure multiplicative model. Compared with low-risk patients, the HR for non-relapse mortality (NRM) using the HCT-CI was 1.3 (95% confidence intervals, 0.7-2.4) for intermediate risk and 1.6 (0.9-2.8) for high-risk patients, and with the MCI was 1.6 (0.9-2.8) and 2.7 (1.5-5.0), respectively. In conclusion, we are introducing the MCI which may have higher discriminating and predictive power for overall survival and NRM. Validation of the HCT-CI and the MCI in larger and separate cohorts of HCT recipients is still needed.