&NA;Fine‐needle aspiration biopsy was performed at laparotomy on 15 patients in whose cases differential diagnosis between colonic diverticulitis and colonic cancer on the basis of preoperative and peroperative examinations was impossible. Histologic examination confirmed the cytologic diagnosis to be correct in 14 cases, in four of them correctly positive for tumor cells. There was one false‐negative result. Culture of swabs taken from 11 patients after puncture showed growth of intestinal bacteria in five cases, but no complication developed in association with or after the punctures.Peroperative fine‐needle aspiration biopsy is a cheap, simple, rapid and safe method that seems to offer a reliable aid to differential diagnosis between diverticulitis and carcinoma. With the use of a rapid staining technique, the result can be available as early as that of frozen‐section microscopic examination.