The aim of the present study was to determine whether the gamma distribution (GD) model is useful in the differentiation of glioblastomas (GBs) and primary CNS lymphomas (PCNSLs). The GD model well described the histological features of PCNSLs and GBs, and its use enabled the significant differentiation of these tumors. The κ, f2, and f3 values were significantly smaller and the f1 values were significantly larger in the PCNSLs than in the GBs. The GD model-derived parameters correlated well with the IVIM-derived parameters. The GD model may therefore contribute to the characterization of brain tumor from the histological viewpoint.