We present 6 cases of spontaneous hemothorax and comprehensively review the medical literature on this subject. We categorize the reported causes and offer a rational diagnostic approach to patients with nontraumatic hemothorax. We recommend specific treatments for specific etiologies, and emphasize the importance of well-established surgical principles for the treatment of hemothorax. Our suggestions should enable physicians to accurately diagnose and expeditiously treat patients with spontaneous hemothorax.