Most adoptees in Japan are adult men.

Adoption in Japan looks quite different than in other places around the world. While the country ranks among the highest in adoptions each year, the majority of adoptees aren’t children — they’re adult men.

The custom is known as mukoyōshi, or “adopted son-in-law,” and it refers to a man being legally adopted by a family, often to carry on the family name and business. Typically this happens when a man marries into the family, though an adult man may also be adopted directly to become a successor.

Before World War II, a Japanese family’s eldest son was legally entitled to inherit the entire family estate. But the 1947 Civil Code abolished that household structure and introduced equal inheritance rights among children and spouses. Even after those reforms, however, many families continued using mukoyōshi adoption to make sure a male would remain the head of the household due to longstanding gendered traditions that favored a male successor to carry on the family’s lineage and assets.

Ronald Reagan was adopted.

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Ronald Reagan was raised by his biological parents, though he did adopt a son, Michael Reagan, with his first wife Jane Wyman.

Mukoyōshi is primarily used for matters of business succession; well-known companies such as Suzuki and Kikkoman, for instance, have involved adult adoption of men to keep running their businesses for years.

The United States is the only country whose annual adoption rate tops Japan’s, but adoption in the U.S. is overwhelmingly focused on children. In Japan, children make up a small fraction of total adoptions — roughly 2% of the country’s approximately 80,000 annual adoptions. In the U.S., by contrast, an estimated 80,598 children were adopted in 2022.

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