A 79-year-old man experienced sudden-onset left hemiparesis and disturbance of consciousness. Diffusion-weighted magnetic resonance imaging showed an acute ischemic stroke in the territory of the right middle cerebral artery. He underwent systemic thrombolysis via the intravenous administration of tissue plasminogen activator (t-PA). Chest radiography and computed tomography performed the following day showed severe hemothorax with atelectasis of the left lung and multiple rib fractures; the initial chest radiogram had revealed rib fractures but we did not recognize them at the time. Conservative treatment with the placement of chest tubes was successful, and the patient recovered without further deterioration. Although systemic thrombolysis with t-PA is an accepted treatment for acute cerebral ischemic stroke, posttreatment intracranial hemorrhage has a negative effect on prognosis. Extracranial bleeding is a rare complication, and our search of the literature found no reports of hemothorax after treatment with t-PA in patients with cerebral ischemic stroke. We have reported a rare case of severe hemothorax after systemic thrombolysis with t-PA. This important complication indicates the need to rule out thoracic trauma with radiography and computed tomography of the chest.