Acute appendicitis is a clinical diagnosis, so it's impossible to have a definitive diagnosis by gold standard (histopathology) pre operatively. The treatment being surgical, negative appendicectomy rates are high. Present study was conducted to evaluate Alvarado scoring system for diagnosis of acute appendicitis and its co relation by histopathology. Retrospective study of consecutive patients admitted with suspected acute appendicitis during the period March 2005 to March 2007. The Alvarado scoring system was computed from admission notes and records and correlated with the histopathology reports. Out of 155 patients, 92 underwent appendicectomy with the intention to treat appendicitis and diagnosis was confirmed in 80 patients. Reliability of scoring system was assessed by calculating negative appendicectomy rate and positive predictive value. The normal appendicectomy frequency was 13% and positive predictive value was 86%. Alvarado scoring system is easy, simple, cheap, useful tool in pre operative diagnosis of acute appendicitis and can work effectively in routine practice.