National Sanatorium Nagashima Aisei-en (国立療養所長島愛生園) was founded in 1930. It was the first leprosy sanatorium funded by the central government, but was the sixth funded by public budget.

According to Dr. Kensuke Mitsuda, the first director of Aisei-en (1931-1957), Aisei-en was modeled after Culion, an island colony of the Philippines, which he had visited in 1921. He pursued the idea of isolating all leprosy-affected people on an island where they would survive away from the rest of the world. He left the National Sanatorium Tama Zensho-en (along with 85 of its residents) to build the new colony, situated on the island of Nagashima in the Inland Sea. Nagashima Aisei-en admitted 2009 patients in 1943. As of December 31, 2015 it had 213 residents, and the average age was 84.2.

The first and only high school for eligible youth living in leprosy sanatoria opened in Nagashima Aisei-en in 1955. It was one of the conditions of the revised Leprosy Prevention Law of 1953. The school accepted entries from all 13 sanatoria, and altogether, 307 students graduated in 29 classes before 1985.

The island of Nagashima was separated narrowly from the mainland and the island of Oku Komyoen. After 17 years of lobbying by the sanatorium residents, the Oku-Nagashima Bridge was opened in 1988 connecting both islands with the mainland.

Nagashima Aisei-en has been active in preserving its own history and runs a history museum which has had over 10,000 visitors. http://www.aisei-rekishikan.jp/