Aim. The aim of the article was to investigate how during the last 25 years of implementation of the new canons law code changed the use of these new law regulations by the church lawyers as well as the mental causes for marital incapacity. Method. The basis of investigation was the analysis of 135 forensic-psychiatric opinions made by the author for the Metropolitan Tribunal of Gniezno in the legal proceedings carried out in the years 1984-2008. Results and conclusions. On the basis of the analysis, the author got the following results. During the first 10 years of implementation of the new canon law code, the legal proceedings were carried on mostly of no 1 or together of no 1 and no 3 canon 1095, but during the last 15 years mostly of no 3 this canon of mental incapacity to undertaking the essentials marital duties. The mental causes of the marital incapacity also changed very significantly in this time. During the first 15 years, there were serious mental disorders such as schizophrenia, epilepsy or oligophrenia, but during the last 10 years the main causes of incapacity to undertaking the essential marital duties were personality disorders, alcohol dependences or psychosexual deviations.