Psychiatrists and psychologists provide consultation to the Catholic Church's marriage courts. Operating under the Church's legal code, these tribunals assess the validity of weddings that have ended in divorce. This report describes one of the standards used for this purpose, the lack of due discretion of judgment, which is concerned with the maturity, understanding, and appreciation that the couple brought to the ceremony. This normal capacity is vulnerable to various mental illnesses, which if present with sufficient severity may nullify the marriage vows as seen by the Church (though not necessarily by the state). Such a finding results in freedom to marry again despite the Church's ban on divorce, provided that due discretion of judgment is regained. Case examples and discussion of the assessment process for due discretion of judgment prepare the consultant to apply psychiatric findings to this unique and urgent legal issue.