Autoimmune hepatitis is a generally progressive, sometimes fluctuating chronic hepatitis of unknown cause that occurs in children and adults of all ages. It is important to distinguish autoimmune hepatitis from other forms of chronic hepatitis, because a high percentage of cases respond to antiinflammatory or immunosuppressive therapy, or both. Appropriate management can prolong survival, improve quality of life, and avoid liver transplantation. This review discusses the pathogenesis, diagnosis, and treatment of this important form of hepatitis.