Medical files filled in by family doctors play in many cases the key role in criminal trials, when the health and life of the victim has been endangered. Family doctors’ patients can play different roles in the trials: the victim or the accused. Sometimes the role of the accused must be played by the family doctor himself. Family doctors must follow several rules, both formal and substantial, to make their medical documents a trustworthy and useful source of information for the courts’ purposes. Knowing the rules of proper classification of injuries for the purposes of law makes it possible for family doctors to complete medical documents in such a way that they become an effective source of information in the forensic opinion giving process.