A total of 1002 patients with cancer of the oesophagus seen at the Finsen Institute, Copenhagen, Radium Centre and/or Department of Surgery, during the 25-year period ending 31.12.1969, were analysed with a view to sex, age, localization of tumour, histology, and survival. The 5-year survival for all seen patients, corresponding to 25% of the cases recorded in the whole of Denmark, was 2.3%, the half-life 5.2 months, and the mean survival 7.5 months. After five years 18 of the 23 5-year survivors succumbed to recurrences. The prognosis is largely independent of sex, age, localization and histological type of tumour. In the present report no regard is paid to treatment, treatment variables being described in part II.