NEW YORK (CNNMoney.com) - Retirees, empty nesters and young professionals usually have little in common, but they're all in the vanguard of a recent trend - they're repatriating center cities.

The trend, which began in the late 1990s, marks a reversal of the post-war urban flight to the suburbs. Now, it's strengthening.

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"I think it's likely to continue for the next 15 years," says John McIlwain, senior fellow for housing at the Urban Land Institute. "Boomers are aging and people think of cities as a good place to retire to, as well as to continue to work."

At a recent teleconference of Coldwell Banker real estate brokers from around the country, the theme was repeated over and over: People are moving back downtown.

In Philadelphia, according to Harry Caparo, CEO of Coldwell Banker Preferred, they're resettling the old downtown core, especially the Rittenhouse Square, Society Hill, Old Town and Museum District neighborhoods.

In Nashville, reports broker David Barnes of Coldwell Banker Barnes, they're moving to the Lower Broad area, where the music clubs and honkytonks are.

Seattle's downtown is also booming, according to Bill Riss, of Coldwell Banker Bain, with high rise apartments and lofts going up at a fast rate.

Young professionals make up a big part of the trend. "It's carefree living," says Caparo. "Young professionals just want to put the key in the door and go to bed at night and lock it up again in the morning." It's also where the action is, professionally and socially. "For them, there's lots of DNA to hook up with," says McIlwain.

Retirees love the museums, restaurants and, most important, access to the best health care. Empty nesters get to live near work.

"For years people traded a commute for affordable housing," says Jim Gillespie, CEO of Coldwell Banker. The further out in the suburbs, the more affordable the homes. But as suburbs expanded and got more crowded, road construction did not, could not, keep up. Congestion grew worse.

"We can't build our way out of road congestion," says McIlwain. "It's a feature of America's suburbs from now on."

So, as soon as they are in a position to do so, many boomers move to avoid all that traffic.

And they can often cash out pricey, suburban homes, buy a great condo in town and still have some money left over.

All the various demographic groups benefit from some of the same aspects of city living. None of them have to cut the grass or water the flowers any more. They don't even have to cook; restaurants are just a short walk or even a phone call away. Leisure time activities, such as movies, plays, concerts, professional sports, art galleries and clubs are nearby and easy to get to.

Of course the ideal of city life is not new. Centuries ago, Ben Johnson said, "When a man is tired of London, he is tired of life."

What kept many Americans away were the social problems that seemed endemic in town - crime, homelessness, poor schools. But cities are much better managed than they used to be, according to McIlwain.

Crime reduction in particular, he reports, has pulled people back. New York, for example, recorded a 75 percent drop in crime from 1990 to 2005. Most cities experienced smaller, but significant, crime reductions.

That's why the latest stats showing an upturn in violent crime are worrisome for city managers. Nationwide, the percentage rise was only 2.5 percent, but it marked the first increase since 2001. Murders jumped: 23 percent from 272 to 334 in Houston; from 330 to 377 in Philadelphia, a 14 percent rise; and 10 percent, from 131 to 144, in Las Vegas.

It may be a sign of things to come. CNN.com reported recently that an "echo boom" effect has led to an increasing population of young males, the demographic most responsible for violent crime.

If felonies spike, that could cause those considering relocating to hit the brakes pretty quick.

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