Fat content evaluation in soft-tissue tumors is based on visual grading of T1-weighted images with uncertain accuracy and inter-rater variability. We used a multi-point Dixon technique to quantitatively measure the distribution of proton density fat fraction in different lipomatous tumors. The effect of radiotherapy on fat content in a myxoid liposarcoma was also assessed, with histograms revealing a distinct alteration. Our data give supporting evidence that maturation of tumor cells is the cause for the lipoma-like areas seen after radiotherapy of myxoid liposarcomas. On a voxel level (2×2×2 mm3) various lipomatous tumors exhibited different fat fraction histograms.