The concealment of a prior marriage at the time of concluding a new marriage contract is one of the challenging issues in Iranian family law, situated at the intersection of custom, jurisprudence, statutory law, and ethics. Adopting an analytical-descriptive approach, this article examines the legal status of concealing a prior marriage and attempts to analyze its effects and legal consequences through the frameworks of the concepts of tadlis (fraudulent misrepresentation) and predetermined condition or implied condition (Shart-e tabani ). In the first section, viewpoints that deem the concealment of a non-consummated marriage permissible based on Article 33 of the Civil Registration Law are examined. These opinions, relying on the removal of marriage records from a duplicate birth certificate, argue that there is no need for disclosure if the wife's virginity is preserved. The article demonstrates that the mentioned article is procedural in nature and cannot serve as a basis for legitimizing concealment in marital relations. In the second section, the prohibition of concealing a prior marriage is examined from two legal perspectives: first, as an instance of tadlis, provided that custom considers a prior marriage history a defect and the intent to deceive is established; second, as a violation of a predetermined condition, in cases where the marriage contract was concluded on the basis of the absence of a prior marriage history. The presented analyses, citing Articles 438 and 1128 of the Civil Code, jurisprudential opinions, judicial rulings, and advisory legal opinions, indicate that if the customary conditions are met and the influence of the characteristic on the mutual consent of the parties is proven, the contract can be annulled. Finally, the article offers suggestions to family court judges, including: a narrow interpretation of Article 33 of the Civil Registration Law and not considering it as a license for tadlis.