Backgroung: This is the first description of the ultrasonographic findings in a cow with vascular hamartoma of the liver. Case presentation: Ultrasonographic examination of a six-year-old Swiss Braunvieh cow revealed an excessive number of hypoechogenic blood vessels in the liver parenchyma and a thrombus in the right hepatic vein. The activities of the liver enzymes and the concentration of bilirubin were within the reference ranges. At postmortem examination, a poorly delineated, non-encapsulated lesion, measuring approximately 10 cm × 10 cm in diameter, was found in the right liver lobe. The cut surface of the lesion was sponge-like and contained extremely dilated blood vessels, one of which was occluded with a branching red thrombus. A vascular hamartoma of the liver with thrombosis was diagnosed based on the histological findings. Conclusions: To our knowledge, this is the first description of the ultrasonographic findings of vascular hamartoma of the liver in a cow. Hamartoma should be considered part of the differential diagnosis in cows with an abnormally large number of blood vessels in the liver parenchyma. This case report broadens the spectrum of liver diseases and ultrasonographic findings of the liver in cattle.