1. Hiatus hernia is a clinical entity, occurring mainly in females in the proportion of about two to one, and mainly in the middle aged or elderly. 2. There are a great variety of symptoms, likely to be confused with upper abdominal conditions and ischaemic heart disease. 3. Radiology will differentiate the former, and radiology and electrocardiography the latter. It is emphasised that in the latter, confusion will rarely arise if a careful case history is taken. 4. Because of the complex neuro muscular mechanism, drugs cannot be relied upon to prevent hernia or, more important, its common complication reflux. 5. Cine radiology at present gives no added information as to the mechanism of hiatus hernia and reflux. 6. The results of surgical repair are disappointing. 7. The operation of vagotomy does not dispose to hiatus hernia or reflux, and, incidentally, in my series proved to be an excellent operation for duodenal ulcer. 8. I suggest, in view of the last two findings that upper abdominal tone plays a part, at least equal to a tight hiatus and strong crura, in preventing hernia and reflux.