Objective: As a part of an evaluation of a large-scale communication skills training (CST) programme, this study aimed to investigate the effect on health care professionals’ (HCPs) self-efficacy (SE) and perceived importance (PI) of the skills taught. Methods: A pre-post intervention design was used, and 1647 HCPs responded to the SE-12 questionnaire. Changes in self-efficacy were examined at an item and scale level. Results: The responses of 74% of the HCPs who replied to at least two of the three questionnaires were analysed. A significant increase in the SE-12 scale scores by 12.45 points between Q1 (baseline) and Q2 (immediately after the intervention) across all professions was found. There was a small albeit statistically significant decrease in the SE-12 scale scores by 2.06 points between Q2 and Q3 (24 weeks after the intervention). Conclusion: The implementation of the CST course significantly improved the self-efficacy of HCPs. The findings were supported by an increase in the number of HCPs who considered the skills that they had acquired to be very important. Practice implications: The findings suggest that the large-scale implementation of evidence-based CST programmes can yield the same outcomes that have been observed in smaller and better controlled studies.