Focal nodular hyperplasia (FNH) of the liver is relatively rare, and can be difficult to differentiate from other benign tumors arising in the liver. We describe a 23-year-old woman and a 25-year-old man with FNH. They were hospitalized for further evaluation of a space-occupying lesion in the liver. Scintigraphy with Tc-99m diethylenetriaminepentaacetic acid galactosyl human serum albumin (Tc-99m GSA) revealed increased radioactivity in the tumor in one patient and radioactivity similar to that in the normal part of liver in the other. F-18 fluorodeoxyglucose positron emission tomography (FDG-PET) showed uptake similar to that of the normal liver in both patients. FNH was diagnosed on the basis of angiographic findings and histological findings in liver biopsy specimens. Our results show that scintigraphy with Tc-99m GSA and FDG-PET may provide information helpful in the diagnosis of FNH.