An analysis was made of 405 appendices removed with the preoperative diagnosis of acute appendicitis. Diagnosis was confirmed histologically in 334 organs. Morphological changes in the appendix were found to correlate with the duration of symptoms. 25% of the acutely inflamed appendices showed significant lymphoid hyperplasia which support the theory that obstruction by lymphoid hyperplasia is important in the pathogenesis of acute appendicitis. Faecoliths, Enterobius vermicularis and schistosomal ova were found in 6.3% and 2.4% of inflamed organs.