Based on a homogeneous series of 40 cases of thoracic or abdominal oesophageal cancer, of which 23 had been confirmed by operation, the authors analyse the contribution of the CT scan to the diagnosis of the extension of the cancer, and evaluate the effects on therapy of this technique. Computed tomography supplies much more precise and complete details of possible cancer extension than any other pre-operative investigation. Conducted after radiological and endoscopic examination of the oesophagus, it supplies rapid, perfectly readable, irreplaceable information on local, regional, and metastatic spread of the cancer. This only slightly aggressive examination enables evaluation of the size of the tumour and its direct relationships, effective exploration of the mediastinal and coeliac glands regions, and detection of possible pleural, pulmonary, or hepatic metastases. Its role in the decision to operate is a considerable one: true assessment of of local, regional, or metastatic extension assists the surgeon in his choice of either curative or palliative therapy. Better still, it enables a route of approach to be decided as a function of data concerning possible extension, as well as the best surgical tactic. As a support for radiotherapy or chemotherapy for this type of cancer, computed tomography greatly assists follow-up supervision.