Forty-two cases of surgically treated pericarditis are presented, with comments on the management and pathophysiology of the acute, recurrent, and chronic stages of the disease. The spectrum of aetiological factors has changed within the last few decades in that tuberculosis is now rare, whereas uraemic pericarditis is referred to surgery with increasing frequency. With the advent of haemodialysis and renal transplantation, these cases should be treated vigorously, since they are amenable to surgical cure. Rapid surgical intervention is advocated in impending tamponade, and in all other acute cases which do not respond promptly to conservative management. In recurrent and chronic pericarditis, surgery is also preferable to long-term medical treatment with steroids and diuretics. Chronic pericarditis should not be allowed to progress to an advanced stage of disease with myocardial involvement and impairment of liver function. Early operation carries little hazard and gives lasting relief in the majority of cases. Microscopical examinations and laboratory analyses point towards an abnormal permeability of capillaries and visceral pericardium as an early and major event in the development of pericardial effusions. Destruction or preservation of the mesothelial cell lining is probably an important factor in determining the progression of acute disease towards adhesions and constriction.