Short answer. No. The Family Code calls marriages between brothers and sisters incestuous and void from the beginning, whether of the full or half blood, and whether the relationship is legitimate or illegitimate. No license, no lapse of time and no good faith on either side can make such a marriage valid.

What the law says

Marriages between the following are incestuous and void from the beginning, whether relationship between the parties be legitimate or illegitimate: (1) Between ascendants and descendants of any degree; and (2) Between brothers and sisters, whether of the full or half blood.

Family Code, Article 37 — Incestuous Marriages. Read the full provision →

Half blood and illegitimacy make no difference

Article 37 closes the two gaps people most often hope are open. The bar covers brothers and sisters whether of the full or the half blood, so a shared father or a shared mother is enough — the parties do not have to be full siblings. And it applies whether relationship between the parties be legitimate or illegitimate, so a sibling relationship that was never formalised on any birth certificate is still a sibling relationship for this purpose. What matters is the blood tie itself, not the marital status of the parents or what any document happens to say.

The other limb: ascendants and descendants

The same article bars marriages between ascendants and descendants of any degree — parent and child, grandparent and grandchild, and onwards up and down the line with no limit. Notice how this differs from the collateral line, where the bar in Article 38 stops at the fourth civil degree. In the direct line there is no stopping point at all. The two provisions also differ in character: Article 37 treats these unions as incestuous, while Article 38 lists relationships void for reasons of public policy, which is where step-relations and adoptive relations are dealt with.

Void from the beginning means exactly that

A void marriage is not a marriage that ends; it is one that never began. Ignorance of the relationship does not save it, and neither does the passage of decades, a license properly issued, a ceremony everyone attended, or children born of the union. The Family Code does not put a prescriptive period on an action to have such a marriage declared void, so the question can be raised long afterwards — commonly when an estate is opened or a second marriage is contemplated. The children's status and the property consequences are governed by their own provisions and are worth separate advice.

If you suspect this in a family history

Article 40 requires a judicial declaration of nullity before a party to a void marriage may remarry, so nobody should treat the invalidity as self-executing and simply move on. The documents that settle the question are the birth certificates of both parties, which show the parentage the article turns on, together with the marriage certificate. Where the birth records are incomplete or contradictory — a not uncommon situation in older civil registry entries — collect what exists and take it to a lawyer before anyone files anything or makes a claim on the strength of the marriage.

Cases citing this provision

These Supreme Court decisions cite the provision above. We list them so you can read them yourself; the summaries of what each decided are not ours to give.

Related provisions

Note. Statute text quoted on this page is reproduced from the official enactment and is linked to the full provision. The explanation around it is general legal information from Vivas & Nobles Law Office, not legal advice. Whether it applies to your situation depends on facts only a lawyer reviewing them can assess.