Three cases of adenocarcinoma of the appendix are reported. All three patients presented with acute appendicitis and the tumors were diagnosed only on histologic examination of the excised appendix. The first patient subsequently had a right hemicolectomy and was proven to have a Dukes' B tumor. The second patient probably had a Dukes' B also, but no further surgery was performed because of advanced presenile dementia. Advanced disease was found in the third patient. Analysis of 145 cases reported over the last ten years suggests that, unless the tumor is in Dukes' A stage, right hemicolectomy should be carried out if the patient is fit for radical surgery. The overall prognosis appears to be the same as that for carcinoma of the colon.