TRENTON, N.J. (AP) – Aided by one of the nation’s largest endowments, Princeton University has decided not to raise tuition, something it hasn’t done in four decades.

The university’s trustees on Sunday decided to keep tuition, both in-state and out-of-state, at $33,000 for the 2007-08 school year. It’s the first time since 1967-68 that annual tuition hasn’t increased.

Tuition at Princeton rose 5 percent, to $31,450, in 2005-06, and it went up another 4.9 percent, to $33,000, for 2006-07.

This time, trustees chose to dip more into the university’s endowment rather than pass more costs on to students, according to Princeton spokeswoman Cass Cliatt.

As of June 2006, Princeton’s endowment stood at $13 billion, with an investment return of 19.5 percent for the year. The return for the previous fiscal year was 17 percent.

Not raising tuition is an unusual occurrence at U.S. universities.

In the present academic year, tuition and fees at private four-year colleges and universities are up an average of 5.9 percent, to $22,218, according to the New York-based College Board. Tuition at public four-year colleges rose an average of 6.3 percent, to $5,836.

Despite Princeton’s holding tuition at present levels, room and board is increasing. For an undergraduate living on campus with a full meal contract, the total cost of going to Princeton will be $43,980 in 2007-08. That’s $1,780, or 4.2 percent more than the present school year.

Princeton also is unlikely in the near future to take a more dramatic step: eliminating tuition.

In an interview with The Associated Press in November, Princeton President Shirley M. Tilghman said doing away with tuition was the “wrong model.”

“With families who have the capacity to make the investment, I think it is right that they be asked to do so,” Tilghman said.