Civil liability for healthcare workers and healthcare institutions is one of the most significant problems in Health and Medical Law. The basis of responsibility is always an open question, whether it be medical errors, misinformation or faulty work organization. Aiming to make things clearer for individuals practising medicine, this paper presents the concept of a professional (medical) error, the basis of responsibility for the doctor (medical error, damage to the patient and the cause-and-effect relationship between a medical error and the damage caused) as well as the precise explanation of who has to prove what in possible court proceedings.