Background and Aims: Acute liver failure (ALF) caused by a sudden loss of liver function in patients without pre-existing liver disease is a rare condition and one of the emergencies in the field of hepatology. The common etiologies of ALF vary in different geographic areas and the course is highly variable among patients with different confounding factors. In this prospective study, ALF patients referred to our tertiary center were followed, and their data were analyzed for determinants of outcome. Methods: From March 2014 through February 2015, all adult and pediatric patients with a diagnosis of ALF, who were admitted to the gastroenterology and hepatology wards of our center with a large liver transplant program, were included in the study. Survivors were followed for at least 3 months after discharge from the hospital. Results: A total number of 45 (23 males) patients were included in the present study. The most common etiology was acute hepatitis A (15.6%), followed by drug induced liver injury (13.3%), and autoimmune hepatitis (11.1%), while most cases were classified as indeterminate ALF (35.6%). Overall survival rate was 71 %; 24.4% (11 patients) died, 46.7% (21 patients) survived without transplant, and 28.9% (13 patients) were transplanted, but 2 of them did not survive. Conclusions: Most cases of ALF in this study had unknown etiology. Acute hepatitis A was the most commonly identified cause. About half of the cases survived without transplantation with very good outcomes after 3 months, one-third received liver transplantation with excellent post-transplant survival.