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.

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.

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.

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.