Two patients are described with hemorrhagic thoracic effusions who required central venous catheterization. Presumed subclavian and internal jugular vein cannulation, ipsilateral to the hemorrhagic thoracic effusions, was confirmed by the operators in each case by the persistent aspiration of blood. Subsequent clinical and radiologic evaluation revealed that the vascular catheters were introduced into the pleural space. In both individuals, the persistent aspiration of extravascular hemorrhagic fluid mimicked intravascular catheter positioning. Physicians treating patients with hemorrhagic thoracic effusions need to be aware of this potential complication that can result in the delayed resuscitation of hemodynamically unstable patients.