Our patient presented with a large liver mass, an extremely elevated AFP level, and an almost certain diagnosis of HCC. However, extensive evaluation and biopsies failed to demonstrate malignancy, and the available evidence strongly suggests that the patient has an adult polycystic disease without renal involvement, and that the mass was the result of hemorrhage and degenerative changes in one of his cysts. Polycystic diseases can involve only one lobe, as it appears in this case. Only about 10-15% of patients with polycystic disease have symptoms due to the liver disease, while 30-50% have associated renal disease. Thus, our patient is unusual in several respects. However, his liver mass has decreased in size, he feels well, and his biochemical abnormalities have returned to normal. Despite a classic presentation for HCC, this case underscores the necessity for a thorough evaluation, especially for patients without major risk factors for hepatocellular carcinoma.