There are two types of proceedings before common courts for annulment of marriages during which expert psychiatrists are appointed. In the first type, the key task of the expert is to assess whether the presence of mental illness or mental retardation at the date of the marriage could possibly pose a threat to the marriage or health of future offspring. The expert performs a retrospective assessment not only of the course and severity of psychiatric disorders strictly distinguished by the legislator, but also their impact on the social functioning of a given person. In the second type of proceedings, marriage annulment is possible when the declaration of conclusion of a marriage was made by a prospective spouse who for whatever reason was in the state that excluded conscious expression of will. The task of the expert in this case is to assess the ability to perform a specific legal act. The aim of the analysis was to discuss problematic and unclear legal formulations concerning marriage annulment, which pose difficulties to psychiatrists and cause that sometimes opinions should only be prepared with a certain probability. Itis particularly troublesome to assess the impactof parent’s mental dysfunctions on the health of future offspring. An additional element hindering the forensic and psychiatric evaluation is an analysis of the influence of the environment (including attitudes and behaviours of a healthy spouse) on the picture and the course of mental disorders of an ill or handicapped prospective spouse.