The paper reports the case of a particularly large retroperitoneal liposarcoma (diameter 60 x 28 x 32 cm, weight 11.200 kg) and focuses on the diagnostic and therapeutic aspects of this tumour. The need for radical surgery to remove the entire mass is stressed, even if it is particularly large; likewise, the patient must be carefully monitored since retroperitoneal recurrence is frequent and must be treated, wherever possible, surgically.