Thrombotic and thromboembolic complications are the main causes of morbidity and mortality in patients with homocystinuria. However, it is unusual for thrombosis to be the single clinical feature leading to investigation for homocystinuria. We report an academically superior teenage boy who presented with sagittal sinus thrombosis, papilledema, transient right hemiparesis, and pneumothoraces. Pyridoxine-unresponsive homocystinuria was diagnosed by aminogram, enzyme assay, and clinical trial. Treatment has been with methionine restriction and betaine. Homocystinuria should be considered in patients with unusual vascular lesions or premature thromboembolism.