Aarethun (born 19 January 1942) is a Norwegian politician for the Labour Party.
From 1964 he worked in the administration of the hospital in his native Lærdalsøyri.
In 1967 he entered Lærdal municipality council.
He was later elected to the county council, first time in 1981.
He became deputy county mayor in 1991, and then county mayor in 1995.