Interferon-alpha therapy is well known to induce a wide range of thyroid dysfunction. A 22-year-old woman with chronic hepatitis C developed overt hyperthyroidism while on interferon-alpha and ribavirin therapy. Tc-99m thyroid scintigraphy demonstrated virtually absent tracer uptake consistent with subacute thyroiditis. Ten months after starting antiviral therapy, overt hyperthyroidism recurred. Repeat thyroid scintigraphy revealed diffusely increased tracer uptake throughout the thyroid gland consistent with Graves disease. This is an unusual case of 2 forms of hyperthyroidism-confirmed scintigraphically and occurring in the same patient over time while on interferon-alpha therapy.