The drop is due primarily to a number of powerful women leaving their corner offices. In the past year alone, more than a third of those women (12) have left their CEO jobs, including a few long-time veterans of the ranking.

As the Fortune 500 list went to print last week, Campbell Soup Co. CEO Denise Morrison announced she was retiring, effective immediately (thus, while Morrison appears on the June 2018 ranking, she is no longer in office). The company did not explain her abrupt departure and did not take questions from analysts on the matter. The 64-year-old had been at the helm since 2011; she was with the company for 15 years.

Another veteran who recently stepped down is Hewlett Packard Enterprise CEO Meg Whitman—the only woman to have run two Fortune 500 companies, the other being eBay. She announced in November that she would be handing over the reigns of HPE to president Antonio Neri. “The next CEO needs to be a deeper technologist,” Whitman said on a call with analysts. “That is exactly what Antonio is.” Whitman has since been tapped to run NewTV, Disney veteran Jeffrey Katzenberg’s new mobile media startup.

Irene Rosenfeld, CEO of Mondelez, announced her retirement last August. She had run the snack food giant for six years, during which time she engaged in high-profile skirmishes with activist investors, including Bill Ackman and Nelson Peltz. She has not announced her next move, telling Fortune last August, “I would simply say the intensity of being on 24/7 is something I will not miss.”

Avon CEO Sheri McCoy also stepped down last August after years of pressure to do so from activist investors Barington Capital Group LP and partner NuOrion Partners; she helmed the company for five years.

Some women have departed after much shorter tenures. Shari Goodman, the only woman to have led Staples, was in the corner office for just over a year. Margo Georgiadis also had a brief tenure as CEO of Mattel, announcing last month that she would be leaving to head the parent company of Ancestry.com.

Other names from our 2017 list that are missing this year: Yahoo’s Marissa Mayer, CST Brands’ Kim Lubel, CH2M Hill’s Jackie Hinman, Ingredion’s Ilene Gordon, Sempra Energy’s Debra Reed, and Reynolds American’s Debra Crew.

Happily, there were also some newcomers to the—far too exclusive—club this year: Ulta Beauty’s Mary Dillon, Kohl’s Michelle Gass, Yum China’s Joey Wat, and Anthem’s Gail Boudreaux. Dillon, who appeared on Fortune‘s list of Most Powerful Women for the first time last year at No. 48, has been running the cosmetics company since July 2013, though this is the first time that Ulta has appeared on the Fortune 500. The other three CEOs have been appointed in the past year.

For a complete list of female CEOs in the Fortune 500, click here.

For daily content on Fortune‘s Most Powerful Women, subscribe to the Broadsheet.