Introduction: Knowledge of the basic legal acts and regulations concerning postmortal organ donation is a crucial issue in ensuring that the will of the potential donors is respected and that physicians are legally protected from potential consequences. This study aimed to assess the awareness and knowledge of physicians and lawyers about the basic legal determinants and criminal responsibility in an opt-out donation model country. Material and methods: Survey-based study involved 100 participants, including physicians (group P; n = 50) and lawyers (group L; n = 50). An original questionnaire consisted of 21 questions about the knowledge of the legal regulations of organ donation in Poland. Additionally, a narrative review of Polish transplantation legal acts was performed to identify potential criminal responsibility related to postmortal transplantation. Results: In the study group all lawyers and 50% of physicians declare that their routine work does not include donors’ death confirmation. 62% of physicians are included directly in donors’ qualification. 92% of lawyers and 90% of physicians suggest that access to knowledge in the subject is not easy. The results of substantive knowledge in the field of transplantation law did not differ statistically between the groups, the median total score in 9 questions test was 5 (3:6) in L and the same in P 5 (2:6). The authors identified four aspects of a physician’s criminal responsibility in the case of postmortal transplantation. Conclusions: This study has revealed that knowledge of the basic legal acts and regulations of postmortal donation, considered to be of paramount importance in ensuring respect for transplant law, needed to be improved. Therefore, further education in these aspects may result in more sufficient protection of physicians from potential legal consequences.