A case of papillary adenocarcinoma arising in Caroli's disease (CD) in a 25-yr-old woman is reported. The diagnosis of malignancy was made by ultrasound-guided, fine-needle aspiration biopsy (FNAB). As there were no metastasis, a liver transplant was performed and the diagnosis was histologically confirmed. Only 22 cases of malignant transformation of CD have been reported to date, all among middle-aged subjects (mean age: 52 yr) of both sexes. Most of these reported cases (83%) were found to be bile duct adenocarcinomas with occasional reports of hepatocellular and undifferentiated carcinomas. Our case is the youngest reported to date and the first to be diagnosed cytologically.