It's the first large American study to show a survival benefit for this easier method of trying to save someone when their heart suddenly stops.
Hands-only CPR uses uninterrupted chest presses to keep blood pumping until paramedics arrive.
Experts say bystanders may be more willing to do CPR if they don't have to do mouth-to-mouth breathing. Hands-only CPR keeps oxygenated blood flowing to the brain and other organs.
The five-year Arizona study looked at more than 4,000 cardiac arrests. It appears in Wednesday's Journal of the American Medical Association.