Homocystinuria is a rare, inherited metabolic disease frequently associated with severe multisystemic involvement such as dislocated lenses, skeletal deformities, mental retardation, and premature vascular occlusion. Arterial and venous thromboembolic events present frequent and life-threatening complications in homocystinuric patients. It has been suggested that mild homocystinemia would be a risk factor for vascular disease. We report a 10-year-old girl with homocystinuria who developed portal vein thrombosis, liver infarction, and pancreatic pseudocyst due to pancreatitis. Possible pathophysiologic mechanisms and suggested treatment are described.