In this article, we present supplementary data to the article entitled "Self-learning training versus instructor-led training in basic life support: a cluster randomised trial" [1]. In three supplementary files, we present the informed consent of the included participants, the modified instrument to calculate the total score for practical skills called "the Cardiff Test of basic life support and automated external defibrillation" and the questionnaire to obtain background factors, theoretical knowledge, self-assessed knowledge and confidence and willingness to act, distributed directly after training and six months after training. The results of comparisons between "directly after intervention" and "six months after intervention", for each training group separately, are presented in three tables. We also present two tables showing the reasons why the participants were not prepared to perform compressions and/or ventilations in the event of a sudden out-of-hospital cardiac arrest.