The chances of surviving an out-of-hospital cardiac arrest depend on early and high-quality cardiopulmonary resuscitation (CPR). Our aim is to verify whether the use of feedback devices during laypersons' CPR training improves chest compression quality. Laypersons totalling 450 participating in Basic Life Support and Automated External Defibrillation (BLS/AED) courses were randomly divided into three groups: group No Feedback (NF) attended a course without any feedback, group Short Feedback (SF) a course with 1-minute training with real-time visual feedback, and group Long Feedback (LF) a course with 10-minute training with real-time visual feedback. At the end of each course, we recorded 1 minute of compression-only CPR. The primary end point was the difference in the percentage of compressions performed with correct depth. There was a significant improvement in the percentage of compressions with correct depth in the groups receiving feedback compared to the other (NF v. LF, p=0.022; NF v. SF, p=0.005). This improvement was also present in the percentage of compressions with a complete chest recoil (71.7% in NF, 86.6% in SF, and 88.8% in LF; p<0.001), compressions with the correct hand position (93.2% in NF, 98.2% in SF, and 99.3% in LF; p<0.001), and in the Total CPR Score (79.4% in NF, 90.2% in SF, and 92.5% in LF; p<0.001). There were no significant differences for all of the parameters between group SF and group LF. Real-time visual feedback improves laypersons' CPR quality, and we suggest its use in every BLS/AED course for laypersons because it can help achieve the goals emphasized by the International Liaison Committee on Resuscitation recommendations.