The general features of acute non-specific (benign) pericarditis are now well known from the large number of cases reported from the United States (Barnes and Burchell, 1942;Carmichael et al., 1951; Scherl, 1956;Chapman and Overholt, 1957) and Scandinavia (Krook, 1954). Accounts from this country are limited to smaller numbers of patients (Davies, 1952;Bower et al., 1953;Will and Fleming, 1958). A clear pattern emerges from these reports and it is not proposed to describe the syndrome in elaborate detail but rather to emphasize certain unusual features and difficulties that have occurred in the present series of fourteen patients.The clinical picture of the ordinary uncomplicated case of acute non-specific pericarditis (ANSP) is usually that of a young man who complains of severe retrosternal pain which is made worse by movement and breathing. The temperature is raised and pericardial friction is present. The electrocardiogram shows uniform elevation of the S-T period in most leads, without abnormal Q waves, followed in a few days by lowering of the T waves as the S-T period returns to the isoelectric level. T wave inversion follows and the tracing then returns to normal ( Fig. 1 and 2). Radiological enlargement of the heart shadow due to pericardial effusion is commonly seen and there may be pleural effusion (Fig. 3). Increase of jugular venous pressure may occur. After a period of days or weeks all the abnormalities disappear and full recovery takes place. An upper respiratory infection often precedes or accompanies the onset of the illness.In the present series five cases followed this course and call for no special comment, but others showed unusual and sometimes puzzling features which will be mentioned in more, detail. All the patients were men and their ages ranged from 19 to 75 years. One patient died (see Table).Pericardial friction is not invariably heard. It was absent in three patients-and in another it was heard on one day only (Case 2). The occurrence of ANSP without friction has been previously noted; there were 13 (26%y) in Carmichael's (1951) 50 patients and 11 (37°4) in Scherl's (1956) 30 patients. No friction was heard in the fatal case of Pomerance et al. (1952).The number of patients who had repeated attacks, sometimes over long periods, is a striking feature of this series. In Case 1 there was a history of 17 attacks of retrosternal pain during 16 years: in two of these a friction rub was heard by doctors and in most of the others by the patient and his wife. In Case 5 there were 8 attacks of pain, 6 of which were observed, during 5 years: friction was heard in only one of the attacks. Another patient, Case 11, had 5 attacks of pain during 8 months but no rub was ever heard. Three attacks occurred in two patients, Cases 3 and 12, and 2 in one, Case 4. Recurrences have been frequently observed and were noted by Carmichael et al. (1951)inprobably 9 (18%) of their patients. Krook (1954)