Step into Frank's bar and you'll get a glimpse of what Halloween is becoming.

The popular tavern in Chicago's Lincoln Park neighborhood has been decked out for weeks in black and orange, and patrons can order drinks with such names as "Sex on a Tombstone." On the night itself, manager Robby Ehlert expects to see a number of costumes that won't be G-rated.

"A lot of the costumes are, uhhh, not costumes kids would wear," he says with a chuckle. "You'll see sexy cops, sexy pirates — anything sexy basically."

Increasingly, Halloween (search) is a holiday for adults, sometimes celebrated with kids but often without them.

"I've never seen a season like this," says Joe Marver, founder of Spirit Halloween Superstores (search), a chain of nearly 200 specialty stores nationwide that open just for the weeks preceding the holiday.

Marver says most adults used to wait until the last minute to throw together a costume. But this year, he's already had to reorder some lines of adult-sized garb. (He, too, says pirates are big this year, apparently due to the movie "Pirates of the Caribbean: The Curse of the Black Pearl." (search))

Adults now represent up to 65 percent of his costume sales, a noticeable shift compared with years past.

"This is an adult holiday," Marver says. "It's party time."

A first-time survey done in recent weeks by the National Retail Federation found that young adults are fueling the trend.

Of those surveyed, 57 percent in the 18-to-24 category said they planned to dress in costume and nearly half said they'd be attending a Halloween party. In the 25- to 34-year-old category, it was 45 percent and 37 percent, respectively.

Survey respondents in their 40s and 50s were more likely to decorate their homes and yards.

"I think our generation is a little more hesitant to let go of childhood than past generations," says Ehlert, the Chicago bar manager, who's 30. "We want to hang onto Peter Pan as long we can."

Heightened adult interest in Halloween has caught the attention of many, from alcohol distributors to nonprofit organizations.

UNICEF — a relief organization that has long relied on young trick-or-treaters to raise funds — now enlists a number of top restaurants to donate $1 for every meal served on Halloween.

Meanwhile, others are carving out their own holiday traditions.

At OrangeYouGlad (search), a three-woman design firm in New York, Halloween is an "official company holiday."

Last year, the trio dressed as "Domo-kuns" — friendly space creatures from Japanese lore — and attended the packed annual Halloween parade in Greenwich Village (search). The following day, they traipsed around town posing for photos with tourists and at city landmarks.

"We love it because we get to be creative and fun," says 36-year-old Monica Hsu, one of the firm's partners. And with all the seriousness of life — war, terrorism, economic woes — she adds, "This is one day when people can let go."

In truth, experts say the traditions that gave rise to Halloween — the Celtic "Samhain" festival and the British All Hallows' Eve — were mainly for adults in the first place.

"The notion that Halloween is simply for kids is a misconception based on the centrality of trick-or-treating in the 1950s, when there was an attempt to take the mischief out of Halloween and 'infantilize' it," says Nick Rogers, a history professor at York University in Toronto and author of "Halloween: From Pagan Ritual to Party Night."

He says the Greenwich Village parade was among the first to re-ignite adult interest in the 1970s. Today, he estimates that two-thirds of adults celebrate Halloween.

New Orleans is another city where masses of costumed adults gather to party on Oct. 31.

Archie and Jane Casbarian watch the festivities with friends from the balcony of the couple's restaurant, Arnaud's, in the city's French Quarter. Each year, they host a formal dinner and costume party for a small group whose children, like theirs, have "flown the coop."

This year, the Casbarians plan to dress as the scarecrow and Dorothy from "The Wizard of Oz." And Archie Casbarian is sure of one thing: "My kids, who are 26 and 28, wouldn't be caught dead with us."

Other young people are glad to share the Halloween fun with the adults in their lives.

Says Richard Hawks, a 13-year-old from Northridge, Calif.: "If my step-mom and dad didn't dress up, I would be disappointed."