During a period of six years 131 patients had CT for gastrointestinal tumours or inflammatory bowel disease; the results were analysed retrospectively according to standard criteria. The preoperative CT appearances were compared with the surgical and histological findings. Confirmation of the diagnosis was obtained at surgery and from pathological studies carried out within six weeks of the CT. There were 93 malignant and 8 benign tumours and 30 inflammatory lesions. The reliability of CT for determining tumour extent and the presence of metastases can be improved by standardising the method of examination. Altogether a sensitivity of 75-85%, a specificity of 89-96% and an accuracy of 83-86% was obtained, depending on the anatomical lesion. Correct findings of all three staging parameters T, N and M for carcinomas was, however, obtained in only 56%. Differentiation between malignant and benign tumours and from inflammatory lesions was possible in the presence of specific CT patterns.