Laura Sessions Stepp, a Pulitzer Prize-winning journalist whose reporting on teenage sex and “hookup” culture on college campuses explored in strikingly intimate detail how adolescent girls and young women think about relationships, love and bodily autonomy, died on Feb. 24 in Springfield, Va. She was 73.

Her husband, Carl Sessions Stepp, said the cause of her death, at a memory-care facility, was from complications of Alzheimer’s disease.

In a series of articles for The Washington Post, and later for her best-selling book, “Unhooked: How Young Women Pursue Sex, Delay Love and Lose at Both” (2007), Ms. Sessions Stepp immersed herself in the lives of her subjects in the Washington area and at several colleges — going to parties, hanging out in dorms and tagging along on trips to the mall.

She earned their trust with a soothing voice accented by her Arkansas roots. But most of all, she listened.

“She wasn’t judgmental,” Henry Allen, her editor in The Post’s Style section, said in an interview. “These girls would tell her these amazing things.”

In July of 1999, readers of The Post woke up to a startling front-page headline: “Parents Are Alarmed by an Unsettling New Fad in Middle Schools: Oral Sex.” Ms. Sessions Stepp had interviewed several teenagers in Arlington, Va., and discovered that oral sex had become a popular way to avoid pregnancy and appear cool.

Some of the girls she spoke to were nonchalant: “What’s the big deal? President Clinton did it,” one quipped.

Others were more circumspect. “I didn’t really know what it was,” one eighth-grade girl confided about the time a boy had suggested it. “I realized pretty soon that it didn’t make him like me.”

Ms. Sessions Stepp’s subsequent articles explored “freak dancing,” the way students “grind” on each other at school dances; “buddysex” among high schoolers; and sexual score cards kept by college women, among them a University of Pennsylvania student who rated her companions and included dates and footnotes.

“These women analyze their numbers as if they were comparison shopping for the right size and color of shoes,” Ms. Sessions Stepp wrote in The Post in 2004. “They tell each other that sex is separate from love. And few adults tell them any different.”

She was blunt but detached in her newspaper articles, telling fly-on-the-wall stories about provocative topics that didn’t normally surface on the front page of a family newspaper. But that detachment all but disappeared when she expanded on her reporting in “Unhooked.”

Now she was worried.

“I hope to encourage girls to think hard about whether they’re ‘getting it right,’ whether their sexual and romantic experiences are contributing to — or destroying — their sense of self-worth and strength,” she wrote in the book’s introduction. “Their studied effort to remain uncommitted convinces me only of how strongly they want to be attached.”

She ended the book with “A Letter to Mothers and Daughters.”

“If you are a woman who came of age during the women’s movement of the 1960s and 1970s, I suspect you believe, as I do, that we have a responsibility to reach out and help other women improve their lives,” she wrote. “This means especially the next generation: our daughters all, moving through adolescence into young adulthood.”

Those admonitions didn’t sit well with some critics, who accused her of being a prudish alarmist.

“It is the time-honored duty of the adolescent to alarm adults (parents, in particular),” Meghan O’Rourke wrote in Slate, “by having wild and often idiotic fun — e.g., streaking naked across campus, playing drinking games, throwing things out windows, hooking up with an acquaintance or a friend who, in a flush of late-night hormones, suddenly looks kind of hot.”

Ms. O’Rourke, noting that she attended college “in the early days of ‘hookup’ culture,” wrote that her “recollection, through the haze of years, was that the whole point of hookups was that they were pleasurable — a little embarrassing, sometimes, but mostly, well, fun.”

Kathy Dobie, a journalist who reviewed the book in The Post, wrote that Ms. Sessions Stepp was “conflating what the girls refuse to conflate: love and sexuality.”

“‘Unhooked’ can be downright painful to read,” Ms. Dobie wrote. “The author resurrects the ugly, old notion of sex as something a female gives in return for a male’s good behavior, and she imagines the female body as a thing that can be tarnished by too much use.”

Ms. Sessions Stepp defended the book in interviews.

“I didn’t want to be a scold, I grew up with scolds,” she told The Baltimore Sun. “And I am not saying, ‘Have less sex.’ I am saying, ‘Have more romance.’ Love is a word that I didn’t hear, along with passion, joy, anticipation, and just being goopily in love.”

Her voice rising, she added: “I am sick and tired of having to defend what I think is a reasonable middle position. The far right wants you to wait until you are married to have sex. The far left is telling you to have as much sex as you want, the only requirement is protection. These young women are in the middle trying to figure out how to do this.”

Laura Elizabeth Sessions was born on July 27, 1951, in Fort Smith, Ark. Her father, Robert Sessions, was a Methodist minister who preached in support of school desegregation, an unpopular position that resulted in a cross being burned in the family’s front yard. Her mother, Martha Rae (Rutledge) Sessions, was a psychologist.

In high school, she dated a lot. Boys picked her up on her doorstep, she recalled in an interview with The New York Times after “Unhooked” was published. Some gave her friendship rings, which her father insisted she return.

She studied German and English at Earlham College, in Richmond, Ind., graduating in 1973. The following year, she earned a master’s degree in journalism from Columbia University.

Her first job was in television news, as a weather reporter. After working at newspapers in Florida and Pennsylvania, she joined The Charlotte Observer in 1979 as an editor overseeing newsroom projects. She led a team of reporters who won the Pulitzer Prize for Public Service in 1981 for a series of articles about brown lung disease among textile workers.

In 1982, Ms. Sessions Stepp joined The Post as an editor, turning to writing four years later. She took a buyout from the newspaper in 2008.

In addition to “Unhooked,” she wrote “Our Last Best Shot: Guiding Our Children Through Early Adolescence” (2000), a well-received book that explored the struggles adolescents face with social belonging, identity, learning and independence.

Her marriage to Robert King ended in divorce.

She married Carl Stepp, a journalist and longtime journalism professor at the University of Maryland, in 1981, and they shared each other’s surnames. In addition to Mr. Stepp, she is survived by their son, Jeff Stepp; two stepdaughters, Ashli Stepp Calvert and Amber Stepp; three grandchildren; her stepmother, Julia Sessions; and her sisters, Teresa Kramer, Kathy Sessions and Sarah Lundal.

Unlike many reporters in Washington, Ms. Sessions Stepp never wanted to cover politicians or other well-known people.

“Chronicling the lives of the rich or famous is a sexy beat,” she wrote in Nieman Reports magazine in 2000. “It wins reporters spots on the front page, not to mention dinner party invitations. But it’s not nearly as personally rewarding, in my view, as writing about ordinary people.”