"Are they or aren't they really veterans?" is a question often asked when encountering a homeless person claiming to be a vet.
There's a good chance they are.
"There is plenty of evidence to show that one-third of [homeless males] are veterans," says John Baskerville of Swords to Plowshares, a non-profit veterans support group in the San Francisco Bay area.
Nearly half of the homeless vets are from the Vietnam era. Eighty percent of them have substance abuse problems.
"I drink," says Richard Smith, a Navy vet. "I'm an Irishman. I drink heavily."
And 45 percent of them are mentally ill and unlikely to get off the streets without treatment.
Brian Roth, a Marine veteran, says he has been hopelessly addicted to drugs since he came back from Vietnam in 1969, and has never had a home of his own.
"Just get me off the street," Roth says. "I'm tired. … I'm 55 years old.
"I'm sleeping with a guy in his van right now," he adds.
According to his records and relatives we spoke with, Roth went to college after his military service and even completed medical school at Michigan State before he started getting arrested for writing illegal prescriptions.
"I know I smell like a skunk and look like one," he says. "But for a year I've been trying to get into a program, and I will stay there if they just make it available."
On any given day there are an estimated 300,000 homeless vets.
"We have a system that is absolutely, positively, totally at capacity," Baskerville says. "It's a struggle every day to try and figure out where we can get services for our veterans."
The Veterans Administration and its network of local government and non-profit organizations can only come up with 100,000 beds each night, enough for only one out of three.
The shortfall is likely to expand as financially strapped municipalities continue to cut public health and housing projects. And a whole new generation of combat veterans is about to hit the system.
"We have to do more," says Anthony Principi, secretary of the U.S. Department of Veterans Affairs. "We have to attempt to increase our funding level to offset the loss of funding at a local level. But what the local level has to do is get those community-based, non-profit, those faith-based organizations to help fill the void."
Non-profit organizations like Swords to Plowshares are already taking care of 95 percent of the housing and treatment homeless vets are getting through a complex combination of the VA, and federal and local subsidies.
"This isn't a problem that gets solved in Washington," says Peter Dougherty, of the Advisory Committee on Homeless Veterans. "It's a problem that gets solved on Main Street and back streets of cities and towns across America."
This story originally was reported on ABC News' Nightline Nov. 11 by Mike Cerre.