Hepatitis A is a nationally reportable condition, and the surveillance case definition includes both clinical criteria and serologic confirmation. State health departments and CDC have investigated persons with positive serologic tests for acute hepatitis A virus (HAV) infection (i.e., IgM anti-HAV) whose illness was not consistent with the clinical criteria of the hepatitis A case definition. Test results indicating acute HAV infection among persons who do not have clinical or epidemiologic features consistent with hepatitis A are a concern for state and local health departments because of the need to assess whether contacts need postexposure immunoprophylaxis. This report summarizes results of three such investigations, which suggested that most of the positive tests did not represent recent acute HAV infections. To improve the predictive value of a positive IgM anti-HAV test, clinicians should limit laboratory testing for acute HAV infection to persons with clinical findings typical of hepatitis A or to persons who have been exposed to settings where HAV transmission is suspected.