Background Decision making with advanced cancer patients is often associated with decisional conflict regarding treatment outcomes. This longitudinal multicenter study investigated German physicians’ course of decisional conflict during the decision-making process for a Simulated advanced-stage cancer Patient (SP). Results were compared to a matched sample of Belgian physicians. Methods German physicians’ (n = 30) decisional conflict was assessed with the Decisional Conflict Scale (DCS) at baseline (t1) and after the four steps of a decision-making process: after reviewing the SP chart (t2), after viewing an assessment video interview with the SP (t3), after reviewing the team recommendations (t4), and after conducting the patient-physician decision-making interview (t5). The results were compared to those of a Belgian matched sample (n = 30). Results Decisional conflict of German physicians decreased during the Decision-Making process (M = 53.5, SD = 11.6 at t2 to M = 37.8, SD = 9.6 at t5, p < 0.001). This was similar to the pattern in the Belgian sample (M = 53.5, SD = 12.5 at t2 to M = 34.1, SD = 10.9 at t5, p < 0.001). There was no significant difference between the two groups for Decisional conflict end scores (p = 0.171). At the end of the Decision-making process, in both groups, still 43.3% of the physicians among each group (n = 13) reported a high Decisional Conflict (DCS > 37.5). Conclusions Physicians’ decisional conflict decreases during the decision-making process for an advanced cancer SP, though it remains at a high level. Culture, language and different health care systems have no influence on this process. The results emphasize the influence of psychosocial factors. We conclude that this issue should be considered more intensively in future research and in clinical care.