Background— Bystander cardiopulmonary resuscitation (CPR) improves survival from out-of-hospital cardiac arrest (OHCA) but often is not performed. We hypothesized that subjects viewing very short Hands-Only CPR videos will (1) be more likely to attempt CPR in a simulated OHCA scenario and (2) demonstrate better CPR skills than untrained individuals. Methods and Results— This study is a prospective trial of 336 adults without recent CPR training randomized into 4 groups: (1) control (no training) (n=51); (2) 60-second video training (n=95); (3) 5-minute video training (n=99); and (4) 8-minute video training, including manikin practice (n=91). All subjects were tested for their ability to perform CPR during an adult OHCA scenario using a CPR-sensing manikin and Laerdal PC SkillReporting software. One half of the trained subjects were randomly assigned to testing immediately and the other half after a 2-month delay. Twelve (23.5%) controls did not even attempt CPR, which was true of only 2 subjects (0.7%; P =0.01) from any of the experimental groups. All experimental groups had significantly higher average compression rates (closer to the recommended 100/min) than the control group ( P <0.001), and all experimental groups had significantly greater average compression depth (>38 mm) than the control group ( P <0.0001). Conclusions— Laypersons exposed to very short Hands-Only CPR videos are more likely to attempt CPR and show superior CPR skills than untrained laypersons. Clinical Trial Registration— URL: http://www.clinicaltrials.gov . Unique identifier: NCT01191736.