AbstractEvery individual experiences good luck and bad luck. Three features characterize medical events associated with good luck or bad luck: There is no control over the event, the event occurs through chance or accident, and the event is of significant interest. These characteristics can be used to develop a working definition of medical luck. Medical good luck and medical bad luck are typically assigned to either the individual or to the event, but assigning these instead to the relationship between individual and event provides the opportunity for intervention. By assigning valences to each individual‐event relationship and summating them, the total good luck or bad luck associated with the event can be determined. Intervening in the medical event by increasing the valence of the significance for each affected individual to the event will increase that event's total good luck. A total valence of zero before or after intervention does not, however, imply absent medical luck but simply a combination of medical good luck and medical bad luck because significance interest in the event persists. Therefore, there is no medical luck simpliciter, only medical good luck and medical bad luck. Medical events are especially helpful to understanding good luck and bad luck, because they are non‐fictional, often generate significant interest, and are modifiable.