A medical emergency is an acute injury or illness that poses an immediate risk to a person's life or long-term health, sometimes referred to as a situation risking "life or limb". These emergencies may require assistance from another, qualified person, as some of these emergencies, such as cardiovascular (heart), respiratory, and gastrointestinal cannot be dealt with by the victim themselves.

Dependent on the severity of the emergency, and the quality of any treatment given, it may require the involvement of multiple levels of care, from first aiders through emergency medical technicians, paramedics, emergency physicians and anesthesiologists.

Any response to an emergency medical situation will depend strongly on the situation, the patient involved, and availability of resources to help them. It will also vary depending on whether the aid occurs whilst in hospital under medical care, or outside medical care (for instance, in the street or alone at home).