A new MRI parameter representative of active tumor burden, the diffusion volume (DV), is proposed in the evaluation of histological grade (G1/G2/G3) and risk classification (low/medium/high-risk) of patients with cervical and endometrial cancer. DV is defined as the sum of the voxels within a tumor with apparent diffusion coefficient (ADC) values enclosed in a specific range and associated to higher cellular density. A semi-automated segmentation procedure was used to calculate the DV. A freehand closed ROI outlined the whole visible tumor on the most representative slice of ADC maps defined as the slice with the maximum diameter of the solid neoplastic component. Successively, two thresholds were generated on the basis of the mean and standard deviation (SD) of the ADC values: lower threshold (LT="mean minus three SD") and higher threshold (HT="mean plus one SD"). The closed ROI was expanded in 3D, including all the contiguous voxels with ADC values in the range LT-HT x 10-3 mm2/sec. The DV of cervical and endometrial cancer allows stratification of G-grade and risk groups, works better than the conventional ADC values and T2 volume in the above stratification and shows an excellent intra- and inter-observer variability.