Abstract How professionals communicate during medical procedures may have a significant impact on children and adolescents’ pain. Rel@x is a manualized training program designed to develop hypnosis-derived communication skills to mitigate childhood pain and distress. The study aimed to evaluate if this training was associated with an improvement and maintenance in communication skills over time, and measure associations between changes and participants’ characteristics. A 9-hour training in hypnosis-derived communication was offered to 78 volunteer healthcare professionals from a tertiary pediatric hospital, and 58 participated in the evaluative study. Participants were evaluated at baseline, immediately after training, and 5 months later (39 ± 10 yrs, 52 women, 54 nurses). We used a video-recorded standardized simulation protocol of blood draw and coded the participants’ interactions with the pre-validated Sainte-Justine Hypnotic Communication Assessment Scale (SJ-HCAS) assessing relational, technical, and total skills. We modeled pre-post-follow-up changes over time with latent growth curve models. Satisfaction with Rel@x was consistently excellent (97%). Across the 3 domains, we observed significant improvements of total (+ 61%, 95% CI 53–69%), relational (+ 27%, 95% CI 20–34%), and technical skills (+ 124%, 95% CI 08–140%). Post-training competence levels were 73–91% across domains. A large proportion of acquired skills were maintained at 5 months (55–75%) suggesting a significant effect of the training. Sensitivity analyses confirmed these results (best-case/worst-case skill maintenance ratio: 59–79%/49–73%). Larger improvements in technical skills were associated with younger age and lower baseline skills of participants. The Rel@x training is associated with improved skills in hypnotic communication post-training and at follow-up. This simulation study paves the way for future efficacy studies to examine the effect of hypnotic communication on real patients’ pain and distress.