Of the CEOs who lead the companies that make up the 2018 Fortune 500 list, just 24 are women.

That number is down 25 percent from last year’s record-breaking 32 female CEOs, the highest share of women since the Fortune’s first 500 list in 1955. While women were at the helm of 6.4 percent of the companies on 2017’s list, that number is now down to 4.8 percent.

The biggest reason for this drop, according to Fortune, is that more than a third of Fortune 500 female CEOs resigned in the past year. That includes several 500 veterans, like Campbell Soup Co.’s Denise Morrison, Hewlett Packard’s Meg Whitman, Mondelez’s Irene Rosenfeld and Avon’s Sheri McCoy.

Four new female CEOs do join the ranks: Ulta Beauty’s Mary Dillon, Kohl’s Michelle Gass, Yum China’s Joey Wat and Anthem’s Gail Boudreaux. This year is Ulta’s first on the list, while the other three CEOs were recently appointed.

Although the Fortune 500 list has been released annually for the last 63 years, it wasn’t until 1998 that Fortune began noting executives’ gender. Since then, the magazine noted that the percentage of female CEOs has generally increased, with several dips after 2011.

The Wall Street Journal recently found, women CEOs still get paid a fraction of what their male counterparts earn. Former Mattel CEO Georgiadis was the highest-paid female CEO of 2017, with compensation totaling $31.3 million. Still, that’s one-third of what the highest-paid male CEO, Broadcom’s Hock Tan, made in 2017 ($103.2 million.)

And as men make up a majority of Fortune 500 CEOs, women still get left out of boardroom decisions. Twelve companies on the 2017 Fortune 500 list have yet to add a single female board member, an analysis by Equilar and CNBC published earlier this year found.

What Fortune noted about women workers in 1956, a year after its first annual Fortune 500 list came out, somehow still rings true today:

“There are more women in executive jobs today than there were 15 years ago, five years ago, or a year ago, and men’s reluctance to give them executive rank seems to be diminishing. That is not to say that the historic barriers against women in top positions have crumbled. But the surface cracks are widening.”