All perfect praise be to Allah the Lord of the Worlds. May His peace and blessings be upon our Prophet Mohammad and upon all his family and companions.
Conjoined twins, commonly known as Siamese twins, are identical twins whose bodies are joined in the womb. This is a rare phenomenon in general births and presents in many forms regarding the number of heads and bodies. In some cases, there are two bodies with one head; in others, two heads with one body; or multiple bodies and heads with varying points of attachment.
The Sharia rulings (Aḥkām) for these twins differ concerning inheritance, the obligation of blood money (Diyyah) and atonement (Kaffārah) in cases of homicide, and the permissibility of marriage to them or between them. In this response, we limit the focus to the ruling on marrying twins who are united from the abdomen downwards but separate from the top. This ruling is determined by two primary considerations:
First: When the twins are considered two distinct individuals
If the twins have two separate heads and brains, and two distinct wills, they are treated as two separate persons. In this case, marriage to them is prohibited for the following reasons:
• For female twins: It would result in the prohibited combination of two sisters in marriage (Al-Jam‘ bayna al-maḥārim).
• For male twins: It would lead to polyandry (a woman having multiple husbands for one body), which is strictly forbidden.
Shaykh al-Islam Zakariya al-Anṣārī (may Allah have mercy on him) stated:
"A single person cannot have two bodies; thus, two bodies realistically necessitate two heads. If there is only one head, then the whole is considered one body." (Asnā al-Maṭālib, Vol.4/P.90).
The implication of this is that the presence of multiple heads signifies independent personalities for each. Conversely, a single head—even with multiple bodies—signifies a single individual. In contemporary times, this distinction is made by referring to medical specialists and utilizing modern technology and precise laboratory analysis to determine the biological nature of the body and whether it constitutes one person or two.
Second: When the twins are considered a single individual
If the body is multiple but there is only one head, or if there are two heads but one is "superfluous" (Zā'id) such that there is only one brain and one will, then this is treated as a single person. In this instance, there is no objection (Lā ḥaraj) to marriage.
Imam al-Shirbīnī (may Allah have mercy on him) stated:
"Subsidiary issues: If [a woman] miscarries two bodies, even if conjoined, two compensations (Ghurrah) are due... because a single individual cannot have two bodies; thus, two bodies realistically necessitate two heads. If there is only one head, the whole is realistically one body, so only one compensation is due.
If she miscarries three or four hands or legs, or two heads, only one compensation is due, because it is possible for them to belong to one fetus, where some parts are original and others are superfluous. It was narrated from Al-Shāfi‘ī (may Allah be pleased with him) that he mentioned a woman who had two heads; she was married for a dowry of one hundred dinars, he looked at her, and then divorced her." (Mughnī al-Muḥtāj, Vol.5/P.370).
In conclusion, the ruling on marrying conjoined twins depends on whether they are classified, according to Islamic Law, as two persons or one.
1. If they are considered two persons, marriage is impermissible.
2. If they are considered one person, marriage is permissible.
The distinction in this matter, based on the aforementioned jurisprudential criteria, must be made by consulting medical experts and employing modern technology and laboratory tests to reach a definitive conclusion on whether the body represents one individual or two.
And Allah, the Exalted, knows best.
