A hitherto undescribed type of the rare "collision" tumours is reported: necropsy in a 77-year-old male patient revealed liposarcoma of the right seminal vesicle in association with anaplastic carcinoma of the prostate. The carcinoma was fused with the liposarcoma as a result of its invasive local growth and had formed deposits in the lymph nodes, bones and lungs. The left seminal vesicle showed localized amyloidosis. A review of the published cases of mesenchymal tumours of the seminal vesicles is presented.