Summary Focal nodular hyperplasia of the liver (FNH) in a fit young Iranian girl of 19 months presented with asymptomatic hepatomegaly. Liver scan and ultrasound examinations demonstrated a space-occupying lesion involving both hepatic lobes. Arteriography revealed a vascular pattern suggestive of liver cell carcinoma with dilated arterial branches and tumour blush on the capillary phase. At laparotomy the large mass involved both right and left hepatic lobes and was not resected. Tissue diagnosis was established by surgical wedge biopsy. FNH should be considered in the differential diagnosis of an hepatic mass in a clinically well child, particularly female, in which the liver biopsy suggests cirrhosis but arteriography favours liver cell carcinoma. If FNH is diagnosed and the lesion is not resected it is recommended that patients be advised against sex hormone therapy as there may be an increased risk of rupture with intraperitoneal haemorrhage.