Purpose: Serious illness communication is a core task in hemato-oncology that require advanced communication skills and can be emotionally demanding. A 2-day course was implemented as a mandatory part of the 5-year hematology specialist training program in Denmark in 2021. The aim of this study was to assess the quantitative and qualitative effect of course participation on self-efficacy in serious illness communication and measure the prevalence of burnout among physicians in hematology specialist training. Methods: For quantitative assessment course participants answered three questionnaires: Self-efficacy Advance care planning (ACP), Self-efficacy Existential communication (EC) and the Copenhagen Burnout Inventory at baseline, 4 and 12 weeks after the course. The control group answered the questionnaires once. Qualitative assessment was performed as structured group interviews with course participants 4 weeks after the course, transcribed, coded, and transformed into themes. Results: All self-efficacy EC scores and 12 out of 17 self-efficacy ACP scores improved after the course, though mostly non-significant. Course participants reported altered clinical practice and perception of role as a physician. The physicians’ confidence that they could find the time to discuss ACP were low and remained low. The prevalence of burnout was high. Burnout levels were non-significantly lower after the course. Conclusion: A mandatory course of formal training can increase physician self-efficacy in serious illness communication and alter clinical practice and perception of roles. The high level of burnout among physicians in hemato-oncology calls for institutional interventions in addition to training.