If you are a man ages 18 through 25 and living in the U.S., then you must register with Selective Service. It’s the law. According to law, a man must register with Selective Service within 30 days of his 18th birthday.
Currently women are not required by law. Only men. This is Un-Constitutional and against due process. In 1981 Rostker v. Goldberg, The Supreme Court found it ok to exclude women, and did not violate the Constitution.
With the revoking of ban on women in combat roles as of January 24th, 2013 by Sec. Def. Leon Panetta. The Selective Service should be a requirement for all sexes living in the United States between ages of 18-25.