Forty years after its discovery, estimation of serum AFP remains a useful test for clinicians involved in management of patients with HCC or chronic liver disease. The test, when used with the conventional cut-off point of 500 ng/mL, has a sensitivity of about 50% and a specificity of more than 90% in detecting the presence of HCC in a patient with coexisting liver disease. New tests that can significantly increase the specificity at lower levels (i.e., between 10 and 500 ng/mL) are available but have, to date, been too complex to be widely applied in clinical practice. Serum AFP estimation may also be useful in monitoring response to therapy, particularly as more effective systemic regimens are becoming available. Indeed, there is preliminary evidence that changes in serum AFP may be a more accurate and sensitive way of determining the degree of response to treatment than conventional imaging procedures that rely on physical determination of tumor size. It may, perhaps, be time to add changes in serum AFP to the conventional imaging criteria for assessing response in clinical trials.