Gastrointestinal (GI) tract neoplasms can be detected, evaluated and staged by computed tomography (CT), especially from high-resolution examinations, but routine CT scanning may occasionally discover GI neoplasms in patients with non-specific symptoms. We therefore evaluated the sensitivity and main signs of CT examinations resulting from routine sessions. In 46 out of 1560 patients who underwent abdominal CT, it was possible to obtain a diagnosis of primitive gastric or colo-rectal tumour by means of barium X-ray and/or endoscopy. The sensitivity rate of CT obtained from the present study was 86% in gastric tumours and 87% in colonic tumours. In gastric lymphoma, infiltrating carcinoma of stomach and rectal carcinoma, the sensitivity rate was 100%. The CT diagnosis of GI neoplasms was based on diffuse or local thickening of the gut on a solid dishomogenous mass showing contrast enhancement. The prevalence of various patterns depends on site of origin and on macroscopic features of the neoplasia. In conclusion the results suggest that abdominal CT, even if performed with a method not specifically devoted to GI tract, has high sensitivity rates and then a high probability of detecting GI neoplasms when unsuspected at time of the examination. In our series 11% of GI neoplasms were initially diagnosed by routine CT examination.