Splenic abscess and retroperitoneal abscess are uncommon, although severe diseases, with a high mortality rate that has been attributed to delayed diagnosis, due to the unspecificity of clinical symptoms. We report two patients with a splenic and a retroperitoneal abscess, respectively, in both cases as an onset of colon cancer. The two patients complained of abdominal pain and fever as onset symptoms. Abdominal ultrasonography was normal in the case of retroperitoneal abscess and abnormal in the case of splenic abscess. CT Scan was diagnostic in both cases. In the patient with splenic abscess. CT Scan established a further diagnostic suspect of colon cancer, which was confirmed by colonoscopy. In the patient with retroperitoneal abscess, diagnosis of colon carcinoma was made during the surgical act. In spite of an adequate, combined medical and surgical therapy, both patients died within a short time after surgery.