The purpose of our study was to correlate the spectrum of radiologic and pathologic findings in a series of patients with biliary hamartomas and known extrahepatic malignancy. Biliary hamartomas were diagnosed in 18 patients with a primary malignant lesion who had liver biopsy for evaluation of possible metastatic disease. Prebiopsy imaging studies included CT in 16 patients and sonography in 11. Imaging studies were reviewed retrospectively and correlated with findings at surgery and on pathologic examination. The hamartomas were classified histologically by the degree of cystic dilatation of bile ducts within the lesion. Radiologically, biliary hamartomas presented a spectrum of findings including one or two circumscribed lesions (5-10 mm in diameter) in four patients; multiple (about five) lesions (approximately 5 mm each) in one patient; innumerable tiny, nearly uniform (2-5 mm) lesions in two patients; and innumerable lesions of varying size (2-15 mm) in three patients. Among the patients with innumerable lesions, the nodules were either uniformly or nonuniformly distributed throughout the liver. In all cases, the lesions were hypodense on contrast-enhanced CT scans and hypoechoic on sonograms. In eight patients, the lesions were not visible by imaging but biopsies were done at surgery when single or multiple tiny nodules were noted on the liver surface. The diagnosis was made by either wedge or core-needle biopsy; fine-needle aspirations were nondiagnostic. Pathologic examination revealed single or multiple hamartomas of varying sizes ranging from solid to largely cystic lesions; the degree of cystic dilatation did not correlate with imaging findings. Visibility on imaging correlated with larger lesion size; small surface lesions were usually occult. Biliary hamartomas cause single or multiple nonspecific hepatic lesions that may mimic metastases. This diagnosis should be considered in patients with a primary malignant tumor when single or multiple small hepatic lesions are seen, regardless of uniformity of size or distribution.