The Concordat between the Holy See and the Republic of Poland was signed in 1993, but ratified in 1998. Year 2013 marks the 15th anniversary of coming into effect of the bilateral agreement. It is a good opportunity to evaluate its provisions. The paper aims to present one of the pieces of evidence from art. 10 sect. 1 no. 3 of the Concordat, namely, the evidence for registering canonical marriage in the State Civil Registry so that the marriage would be a subject to such effects as a marriage contracted according to Polish law. From the interpretation of the provision in question and application of its norms there arise some theoretical and practical problems. The author tries to solve them and give some postulates de lege ferenda so as to make the law more clear.