Mild elevations in levels of the liver enzymes alanine transaminase and aspartate transaminase are commonly discovered in asymptomatic patients in primary care. Evidence to guide the diagnostic workup is limited. If the history and physical examination do not suggest a cause, a stepwise evaluation should be initiated based on the prevalence of diseases that cause mild elevations in transaminase levels. The most common cause is nonalcoholic fatty liver disease, which can affect up to 30 percent of the population. Other common causes include alcoholic liver disease, medication-associated liver injury, viral hepatitis (hepatitis B and C), and hemochromatosis. Less common causes include α(1)-antitrypsin deficiency, autoimmune hepatitis, and Wilson disease. Extrahepatic conditions (e.g., thyroid disorders, celiac disease, hemolysis, muscle disorders) can also cause elevated liver transaminase levels. Initial testing should include a fasting lipid profile; measurement of glucose, serum iron, and ferritin; total iron-binding capacity; and hepatitis B surface antigen and hepatitis C virus antibody testing. If test results are normal, a trial of lifestyle modification with observation or further testing for less common causes is appropriate. Additional testing may include ultrasonography; measurement of α(1)-antitrypsin and ceruloplasmin; serum protein electrophoresis; and antinuclear antibody, smooth muscle antibody, and liver/kidney microsomal antibody type 1 testing. Referral for further evaluation and possible liver biopsy is recommended if transaminase levels remain elevated for six months or more.