In order to investigate to what extent various determinants in the decision-making process for the treatment of severely ill incompetent patients are influenced by cultural and sociopolitical factors, 540 physicians in Austria, Germany (East and West), and Sweden, countries representing different healthcare systems, were surveyed using a self-administered questionnaire. It provided three case vignettes with different levels of information about the patient's treatment wishes in case of incompetence in a life-threatening situation. We found a general trend to a lower level of treatment in line with the patient's wishes when the information provided was more detailed. Remarkably, a substantial number of doctors did not comply with the patient's wishes. Ethical concerns and patient's wishes appeared as the most important factors whereas religious beliefs of the physician and hospital costs scored lowest. Because of the variability of treatment decisions and the importance of various factors determining the decision-making, an advance directive may be a feasible way of reducing the number of conflicts in critical situations. We recommend that ethical issues of clinical practice should be emphasized in the medical curriculum and in the training of physicians.