A quantitative study of the plain X-ray in the acute abdomen, written from the point of view of the surgeon rather than the radiologist, is presented. Three questions are asked: 1. Which radiological signs are present in the plain X-ray in the acute abdomen and with what incidence? 2. Should plain X-rays be routinely performed in the acute abdomen? 3. Who should report the acute abdominal X-ray? All patients entered into the study were managed personally by the author. In the first part of the thesis, the plain abdominal X-rays of a series of patients (277 in all) suffering from each of the five most common acute abdominal diseases were reviewed for specific radiological features to assess the relative incidence and importance of each sign. In the second part of the thesis 249 consecutive patients admitted to hospital with an acute abdomen due to all types of disease were studied, and the plain abdominal X-rays of each assessed for their value in diagnosis. In the third part of the thesis, a questionnaire of 50 plain abdominal X-rays was answered by surgeons and radiologists of varying clinical experience and the scores of each group compared. The results of the study showed that: 1. Specific radiological features were found in not less than 4% of the X-rays of the five acute abdominal diseases studied in detail. 2. When performed routinely, 'positive' help was obtained from the acute abdominal X-rays of 42% of the 249 patients studied. An argument is presented for the inclusion of the plain X-ray as a routine in the acute abdomen. 3. The plain abdominal X-rays should be reported by a senior radiologist at the time of the investigation, if maximum benefit to both patient and surgeon is to be obtained.