Acute appendicitis is usually encountered clinically as acute abdomen. Typical cases are easy to diagnose, but sometimes it is very difficult to make a diagnosis in atypical cases. The objective of the study was to determine the diagnostic accuracy in patient of clinically diagnosed acute appendicitis. This prospective study conducted in Mymensingh medical college hospital on 1136 patients presented with acute abdomen and clinically diagnosed as acute appendicitis from July 2004 to June 2010. Emergency appendicectomy was done in all consecutive patients after relevant investigation. Intraoperative findings along with histopathological reports were compared with clinical diagnosis. On the basis of histopathological report, 85.65% were found to have acute appendicitis with misdiagnosis in rest of the subjects requiring unnecessary explorations. Negative exploration was more in emergency than office hour. This may be due to diagnostic inaccuracy and decision-making in the management of the acute appendicitis. Management errors can be significantly reduced by accurate preoperative diagnosis of acute appendicitis by improving clinical skill and appropriate investigations.