A private opinion is a statement referring to the expertise not obtained from an expert appointed by the court. Consequently, in medical proceedings this opinion is not as important as expert evidence within the meaning of Article 278 § 1 of the Polish civil procedure. Nevertheless, the role of a private opinion in civil medical litigation is constantly increasing. This is primarily due to the crisis of the institution of an expert witness. The author focuses on the issue whether a private expert has the right to access information gathered in medical records. In the case of consent given by the patient himself as the holder of the right to access medical documentation, this issue does not raise any doubts. The situation is problematic when a medical entity acting as an opponent of the patient intends to use medical documentation to draft a private opinion. The medicinal entity may process sensitive data contained in medical records for purposes strictly defined by law. In view of this dilemma, the author presents the thesis that both the patient and the medical entity have the right to use this evidence if it is based on medical documentation. Her view is based on the content of Art. 27 par. 2 point 5 of the Data Protection Act, which allows to process data necessary to enforce the rights before a court as well as data referring to the principle of equal treatment in civil proceedings.