Introduction: The surgeon considers abdomen as an enigma because in a good proportion of his cases, the cause of abdominal pain or the nature of the abdominal lump, may not be decided in spite of all possible investigations. But application of anatomical knowledge makes diagnosis more interesting and more rational except in few cases. Objective: To assess the diseases in patients with Non-Traumatic Acute Abdomen. Materials and Methods: It is a prospective study. Two hundred cases of nontraumatic emergency laparotomy patients were studied in Different surgical units of Dhaka Medical College Hospital during the period of July 2007to June 2008. The peak age incidence was found in the third decade of life (34%). Overall male-female ratio was 2.3:1, but there were disease specific variations. Acute abdominal pain was the constant symptom with different degree of severity, presenting either locally or diffusely. In conditions with peritonitis either local or diffuse, muscle guarding, rigidity or diminished bowel sound were found. Results: In the present study 200 patients were included. All these patients underwent emergency laparotomy with the provisional diagnosis of acute abdomen. Conclusion: The most common cause of acute abdomen in the study was acute appendicitis, affecting young population; this was followed by Hollow viscus perforation with peritonitis and bowel obstruction. To evaluating patients with acute appendicitis and peritonitis, plain x ray abdomen high sensitive in bowel obstruction and peritonitis as well. USG abdomen had high specificity as well as positive and negative predictive value in acute appendicitis. Acute appendicitis was the commonest cause 48% of patients presenting to Emergency and Casualty as acute abdomen. It must be remembered that 'Diagnostic errors at the initial assessment may at best result in unnecessary surgical intervention, and at worst demise of the patient or a protracted illness due to the development of complications, ......