Helen Gurley Brown, who as the author of “Sex and the Single Girl” shocked early-1960s America with the news that unmarried women not only had sex but thoroughly enjoyed it — and who as the editor of Cosmopolitan magazine spent the next three decades telling those women precisely how to enjoy it even more — died on Monday in Manhattan. She was 90, though parts of her were considerably younger.

The Hearst Corporation, Cosmopolitan’s publisher, said in a news release that she died at NewYork-Presbyterian/Columbia hospital after a brief stay there. She lived in Manhattan.

As Cosmopolitan’s editor from 1965 until 1997, Ms. Brown was widely credited with being the first to introduce frank discussions of sex into magazines for women. The look of women’s magazines today — a sea of voluptuous models and titillating cover lines — is due in no small part to her influence.

Before she arrived at Cosmopolitan, Ms. Brown had already shaken the collective consciousness with her best-selling book “Sex and the Single Girl.” Published in 1962, the year before Betty Friedan ignited the modern women’s movement with “The Feminine Mystique,” it taught unmarried women how to look their best, have delicious affairs and ultimately bag a man for keeps, all in breathless, aphoristic prose. (Ms. Brown was a former advertising copywriter.)