Background: Acute appendicitis is the most common cause of acute abdomen in young adults. In recent years, studies emerged showing that elevated serum total bilirubin levels could indicate a complicated case of acute appendicitis. An elevated serum total bilirubin that is not explained by liver disease or biliary obstruction can be present in many patients of acute appendicitis.   Patients and methods: This is a prospective interventional non-randomized non-controlled study conducted on 175 consecutive cases of acute appendicitis admitted to the emergency unit in the Department of General Surgery at Ain Shams University hospitals, Cairo, Egypt in the period from July 2014 to August 2016. Liver function tests were done as a part of the preoperative investigations. Clinical diagnosis was confirmed postoperatively by histopathological examination. Their clinical and investigative data were analyzed, The level of significance was set at P< 0.05.   Results: Serum total bilirubin was found to be significantly elevated in cases of complicated acute appendicitis.   Conclusion: Serum total bilirubin is a new important adjunct in the diagnosis of complicated acute appendicitis.