The man, a long-term smoker, suffered stroke damage to a part of the brain called the insular, and quit, telling researchers his body "forgot the urge to smoke".
Nasir Naqvoi at the University of Iowa and Antoine Bechara at the brain and creativity institute at the University of Southern California have since identified other patients who quit smoking suddenly after experiencing similar brain damage.
The discovery gives neuroscientists fresh insight into the complex neurological circuitry of the addiction. While neurosurgeons are not about to tackle smoking addiction with a scalpel, it may give scientists clues for developing drugs to combat addicts' urges.
The scientists trawled a database of patient records to investigate the effects of brain damage on behaviour. Their results are published in Science today.
Of 69 smokers who had experienced brain injury, 19 had damage to the insular. All had been smoking at least five cigarettes a day for more than two years. Thirteen with insular damage had quit smoking, 12 suddenly, and had no urge to smoke since. Of 50 patients with damage to other parts of the brain, only four had quit, often after considerable effort.