INTRODUCTION Although harness suspension trauma has been documented since the 1960s, especially in the mountaineering setting, there is little robust medical research into the area. Helicopter hoist rescue shares similar risks and is reserved for those cases that cannot be accessed safely by other routes, where extrication may be hazardous or will take an unreasonable amount of time. The single sling or chest harness used for hoist rescue is a single harness around the upper torso and is easier and quicker to apply than a stretcher. However, the risks of a chest harness need to be balanced against the patient's condition, the environment, aircraft performance, and the urgency of the rescue. CASE REPORT We report an adult male falling 80 ft to his death while being hoisted into a rescue helicopter for a likely fractured ankle. A single rescue sling harness technique was used, but the patient became unconscious, slipped out of the harness, and fell. He had significant comorbidities, including cardiomyopathy, obstructive sleep apnea, morbid obesity, and diabetes. DISCUSSION A decrease in cardiac output secondary to thoracic compression was the presumed cause for his loss of consciousness and the potential physiological mechanisms and modifying factors are discussed. Further research into harness suspension trauma is required. Stretcher, double point harnesses, or rescue baskets are likely safer methods of hoisting, especially in a medically compromised patient. Biles J, Garner AA. Loss of consciousness during single sling helicopter hoist rescue resulting in a fatal fall. Aerosp Med Hum Perform. 2016; 87(9):821-824.