CHICAGO — There are young ones, old ones, thin ones and fat ones. Some show up in chicken suits, others in G-strings. There are highly trained athletes, of course, but also many people who look like a starting line is, well, the last place they should be.

These days, big-city marathons cast an increasingly wide net, drawing tens of thousands of serious and not-so-serious runners to prestigious races in New York, Chicago, Boston and elsewhere.

The incentive to draw as many people as possible is clear enough: The 26.2-mile marathons generate millions of dollars for cities that host them, as well as for the sporting-goods industry.

"The bottom line is marathons today are big business," said Patrick Moscaritolo, head of the Greater Boston Convention and Visitors Bureau.

But after a brutally hot Chicago Marathon descended into disarray this past weekend — with hundreds of runners vomiting or collapsing and organizers forced to call off the race — questions have been raised about whether marathons have become too all-inclusive and too focused on money.

They certainly have grown — and fast.

The number of people taking part in the Boston Marathon, for instance, has more than doubled over the past decade, despite the race requiring qualifying times for most runners. From 1997 to 2007, the number of runners grew from 10,471 to 23,869, said Boston Marathon spokesman Marc Chalufour.

The Chicago Marathon, which has no qualification requirements, has grown from around 16,000 runners pre-registering in 1997 to around 45,000 pre-registering for Sunday's marathon. The actual number of runners was estimated at 36,000 because 10,000 entrants didn't show up at the starting line.

The boom began back in the 1970s when runners Bill Rogers and Frank Shorter helped to popularize marathons in the United States.

"Today, the marathon has become the everyday man's or woman's Mount Everest," said Richard Finn, the spokesman for the New York Road Runners, which organizes the New York City Marathon. "It's a physical challenge, it's something you can be proud of — beat your chest about later."

But the extreme runs can also be dangerous, as evidenced by the hundreds of runners who suffered heat exhaustion and heat stroke during Sunday's race in Chicago. Marathon purists say novices can be prone to those problems and crowd courses for more serious runners.

The cities that host marathons must balance those concerns against what the races bring in.

The Boston Marathon is the city's single-largest event in numbers of visitors it attracts and the exposure it gives Boston as a tourist destination. More than 500,000 people show up to cheer on the runners.

"It is the unofficial kickoff of our visitor season after we've been through winter and, usually, snow as well," Moscaritolo said.

Finn said the same is true of the New York City Marathon, which takes place on Nov. 4.

"It's a very special day," he said. "It is a picture postcard that we send around the world. It says, 'Come to New York!"'

There's civic pride, and then there's the money.

According to Boston's visitors bureau, revenue generated by the Boston Marathon is now more than $50 million. Based on its $110 entrance fee alone, the Chicago Marathon stood to make around $5 million for this year's race — all of which goes toward covering costs of staging the event.

The amount of money injected into the Chicago economy from hotels and restaurants is probably somewhere around $20 million, said Allen Sanderson, a sports economist at the University of Chicago.

"The advantage to a marathon is that two-thirds of the runners are not from Chicago, so you're bringing new money in," he said.

Marathoners also tend to have more spending power than average, and so are ideal targets for many companies' goods and services, hawked at the fitness expos held near the marathon date.

"If you go in there, I have never seen as many American Express Gold and Platinum cards in one place," Moscaritolo said of Boston's expo. Marathoners "are at the top of the bar when it comes to income, profession, education, traveling."

The monetary interests, including how much money is raised by charity groups affiliated with the marathon, can make it hard for organizers to scale down a marathon or to consider calling it off.

Chicago organizers have defended the size of Sunday's marathon, saying they have years of success with large crowds. They insist they provided enough water and sports drink for runners, even though many complained they were left to scrounge for water themselves after some aid stations ran out.

Maryann Caponi, a marathon spokeswoman, says organizers haven't considered reducing the number of entrants, but she wouldn't rule out that possibility.

The Los Angeles Marathon has doubled in size since it began in 1986, with 24,750 people running in March to downtown from the San Fernando Valley.

The LA Marathon can accommodate 50,000 to 75,000 runners because of the city's wide streets, but organizers decide on a cutoff number every year based on staffing levels and number of volunteers, said race president Dr. William Burke.

"You always want to be the biggest and baddest in town, but you can't do that," Burke said.

The Marine Corps Marathon, which runs through Washington, D.C., has seen its numbers fluctuate over the years, from 18,500 in 1997 to as high as 34,000 a few years ago. The cutoff went back down to 30,000 this year.

Public relations coordinator Beth Johnson said organizers allowed the larger crowd as an experiment. "We liked it," she said. "But we liked it a little smaller better."

Associated Press writers Rodrique Ngowi in Boston, Howard Fendrich in Washington and Alicia Chang in Los Angeles contributed to this report. Editor's note: Associated Press writer Michael Tarm participated in Sunday's Chicago Marathon.