Cross-sex reassignment by spouses, whereby the husband becomes a woman and the wife becomes a man, raises significant questions concerning the continuity of marriage. Using a descriptive-analytical method and drawing on jurisprudence, principles, and Iranian law, this study examines whether the continued existence of sexual differentiation is sufficient to preserve the original marriage. Since the marriage was initially valid, the legally accurate characterization of the subsequent effect is automatic dissolution rather than invalidity. The continuity theory relies on the preservation of sexual difference, the presumption of marital continuity, and the distinction between conditions of validity and continuity. the personal nature of marriage, the constitutive roles of husband and wife, and the principle that contracts follow intentions support automatic dissolution. Personal istiṣḥāb cannot establish a relationship with reversed marital roles because the subject matter lacks customary identity, while generic istiṣḥāb cannot prove the creation of a new marital relationship. Caution in sexual matters does not independently establish dissolution but does not justify continuing the relationship without a new contract. Accordingly, the first legally effective reassignment dissolves the marriage, and the other spouse’s subsequent reassignment cannot revive it. Accrued dower and maintenance remain enforceable, whereas future maintenance and spousal inheritance cease.