Millions are about to get health insurance. But are there enough doctors?

“If you do the math, it just doesn’t work,” says Matt Salo, executive director of the National Association of Medicaid Directors. “There is no way we can meet all this new demand with the existing workforce unless we radically change the way we deliver health care.”

American physicians have flooded into subspecialties in recent decades, leaving a dearth of internists and family practitioners to help people manage their health. Some 55 million Americans already live in what the government calls primary care shortage areas. It would take 15,000 primary-care doctors just to fill the current gap, and 45,000 to care for the people will gain health coverage by 2025. Even under the rosiest scenarios, the number won’t rise by more than 6,000—and it may actually decline. “As the demand for adult primary care explodes,” health care experts Thomas Bodenheimer and Mark Smith write in the November issue of Health Affairs, “the capacity to provide that care is shrinking.”

The consequences could get ugly when newly insured people start seeking care next year. Some will discover that their local internists aren’t accepting new patients—or that none of those with openings accept Medicaid patients. And folks who do find doctors may have to wait weeks, or even months, to get appointments for non-emergencies. If a malfunctioning website can nearly derail health care reform, imagine the fallout when people with brand-new insurance policies discover they can’t get routine care.