TUCSON, Ariz.

Congratulations, Shannon Tighe. You are a University of Arizona graduate. But you have no medical insurance.

Tighe is one of the many newly independent high school and college graduates who are without health insurance.

"Each year, millions of students graduate from high school and college, and, for the most part, many don't realize and their parents don't realize they become one of America's largest groups of uninsured," said Ellen Laden, public relations director of Golden Rule Insurance Co., based in Indianapolis.

The most recent report on Arizona's uninsured showed that 266,800 people ages 19 to 29 have no medical coverage. That's nearly 30 percent of that age group, and it represents the highest rate among all age groups, according to Families USA, a nonprofit, nonpartisan group based in Washington, D.C.

Tighe had been covered by her parents' insurance since she was a child, "but as soon as you no longer have a transcript to show, you're off," said the 22-year-old, who received her sociology degree in May.

The Commonwealth Fund, a private, New York-based foundation, reported last year that young adults are the fastest-growing group of uninsured. Nearly 40 percent of the nation's college graduates will be uninsured the first year after they leave campus, the foundation found.

And this doesn't affect only college grads.

The 51 percent of high school graduates nationwide who opt out of attending college will find themselves instantly uninsured, according to the same group. Reasons for lost coverage vary.

Many are late to learn they lose coverage once they are no longer enrolled full time. Others are uninsured after becoming self-employed or taking a job with a probationary period for benefits.

Then there are those who sign up for insurance through their college or university but don't seek coverage once their plan typically runs out during the summer after graduation.