In which countries is sibling marriage legal?
Executive summary
Sibling marriage is banned in the overwhelming majority of jurisdictions worldwide, but reporting shows a narrow set of exceptions and a larger set of countries that do not criminalize consensual incest even while often forbidding marriage between siblings; the clearest, repeatedly cited exceptions for legal marriages involving siblings are limited to half‑siblings in Sweden and Brazil, while the broader question of whether incest is criminalized or marriage‑eligible varies and is reported inconsistently across sources [1] [2] [3] [4].
1. Most countries prohibit sibling marriage — the global baseline
Legal summaries and encyclopedic treatments emphasize that sexual relations and marriages between close blood relatives (siblings, parents/children) are criminalized or explicitly forbidden as marriage impediments in most states, with statutory prohibitions common across Europe, North America and many other jurisdictions [5] [4] [1]. Internationally, statutes typically treat sibling unions as incest or as a marriage impediment because of consanguinity rules and public‑policy concerns such as genetic risk and family integrity [5] [4].
2. A tiny number of documented marriage exceptions: half‑siblings in Sweden and Brazil
Several sources converge on a specific, narrow legal allowance: Sweden and Brazil are regularly cited as permitting marriage between half‑siblings under the civil code or its interpretation, making them the clearest examples where a sibling relationship (specifically half‑siblings) can legally yield a recognized marriage [1] [2] [3]. These sources treat the allowance as limited (half‑siblings rather than full biological siblings) and contingent on domestic marriage law procedures rather than a broad social acceptance [1] [3].
3. Distinction: incest decriminalized versus marriage allowed
A larger group of countries is reported to have no criminal statute against consensual incest between adults or to not define incest clearly in penal law — examples cited include France, Belgium, Luxembourg, Argentina, Japan, Portugal and others — but in many of those places marriage between siblings is still either explicitly barred or practically impossible under marriage law [4] [2]. Thus “incest is not a crime” in a penal sense does not automatically mean “siblings can marry”; many sources stress this legal distinction [4] [6].
4. Conflicting and uneven reporting — interpret claims cautiously
Public lists and forums disagree on which countries permit sibling marriage, sometimes conflating decriminalization of incest, permissibility of sexual relations, and the separate civil‑law question of whether a state will register a sibling marriage; some outlets list Argentina, Russia, Spain, the Netherlands or others as permitting incestuous relationships or not criminalizing incest but do not reliably show that sibling marriage is legally recognized there [4] [2] [6]. Secondary sources and community posts repeat claims (e.g., Argentina) that are not uniformly corroborated by primary statutory citations in this reporting, so those claims should be treated as disputed in the absence of direct legal texts [4] [6].
5. What the sources cannot firmly establish
The assembled reporting reliably supports the broad rule that sibling marriage is prohibited in most countries and that Sweden and Brazil allow marriages between half‑siblings; beyond that, lists of additional countries where “incest is legal” or where siblings “can marry” diverge and often fail to distinguish criminal law from marriage law or to cite primary statutes, leaving room for error [1] [2] [3] [4]. Where precision matters — for example, whether a specific jurisdiction truly permits full‑sibling marriage or only tolerates consensual relations without criminal penalty — consultation of that country’s civil‑code marriage impediments and penal code is required, because the secondary sources here are inconsistent [5] [4].