We evaluated the predictive value of the D-index for pulmonary infection in the early phase of reduced intensity stem cell transplantation (RIST). Out of 68 patients, ten patients developed a pulmonary infection within 100 days after RIST. Both the D-index and the cD-index were higher in the patients with pulmonary infection than in the control group (P = 0.009, P = 0.042, respectively). The best sensitivity and specificity, calculated with receiver operating characteristic curves, showed that the D-index was superior to the duration of neutropenia in predicting pulmonary infection. We also evaluated the utility of a cumulative D-index until 21 days after RIST (D21-index). The D21-index was higher in the patients with pulmonary infection (P = 0.047). The cutoff value of the D21-index was lower than that of the D-index (8650 vs. 11000) with comparable sensitivity and specificity. Our results demonstrate that the D21-index, as well as the D-index, are useful tools for the prediction of pulmonary infection in RIST.