Yes, Demi Moore (born Demetria Gene Guynes on November 11, 1962 in Roswell, New Mexico) really did shave her head for her role as Jordan O'Neill in G.I. Jane.
The movie premiered on August 22, 1997, was directed by Ridley Scott, and starred Viggo Mortensen, and Anne Bancroft, along with Moore.
In August 2012 Insider.com asked her about buzz-cutting her hair down to her scalp, and how it affected her. She told them that at that point she had no mental attachment to her hair, and that she had been involved in the project for so long, and became so committed to the film that her hair meant nothing to her.
Of course the buzz these days is about Ashton Kutcher dating 29 year old Mila Kunis (recently voted the Sexiest Woman Alive by Esquire magazine); Kutcher and Moore are still legally married, though separated.