70 retroperitoneal tumors (10 with an adipous origin out of which 8 were lipomas) have been operated upon in our clinic since 1985. Four cases of giant lipomas are presented in this paper. They weighed 4.5-7.5 kg. and had a diameter over 15 centimeters. Their close proximity with the kidney, duodenum, colon, inferior vena cava etc made there extirpate difficult. The post-operative condition of the patients was good. Although the histopathological tests proved that all these giant lipomas were benign after two to four years, their relapse required a new surgical intervention. The histopathology of the relapsed lipomas revealed a malign degeneration in 3 out of the four cases. The origin of this malign degeneration was in the fibrous part of the tumors.