Hemothorax is a collection of blood in the pleural cavity and is characterized by a pleural fluid hematocrit greater than 50% of the blood hematocrit (peripheral).

Hemothorax is generally related to chest wall trauma or thoracic instrumentation, although it can also result spontaneously, from malignancy, from vascular issues such as aneurysm, arteriovenous malformations, embolisms, or dissections, and from a variety of uncommon diseases.

Symptoms may include anxiety, chest pain, a rapid heart rate, clammy skin, shallow breathing, and shortness of breath. Patients may go into shock.

Complications may include pneumothorax, fibrosis of pleural membranes, infection, shock, and death in the most severe cases.

Tube thoracostomy drainage is the major method of treatment.