The real reasons NCIS stars quit the show – Pauley Perrette, Mark Harmon, Michael Weatherly, more

Pauley Perrette played fan-favorite forensic scientist Abby Sciuto for more than 15 years but left the show at the end of season 15.

Her exit came as something of a shock to fans. On the show, her character resigned after an assassination attempt, but according to multiple reports, the real reason she left was because she had fallen out with series lead Mark Harmon.

The two stars reportedly had a number of clashes behind the scenes in 2016 after the Gibbs actor brought his dog to set, where it bit a crew member leaving him needing 15 stitches. Tellingly, the pair did not share the screen together during Pauley's emotional final episode. Instead, Abby bid farewell to her other colleagues at NCIS HQ and simply delivered a letter for Gibbs and watched from the street as he read it.

In the days following the episode's broadcast, Pauley took to Twitter with a series of vague tweets which seemingly referenced the incident.

Executive producer Charles Floyd Johnson has since addressed Pauley's exit. Recalling an on-set incident that sparked tension, he told The Hollywood Reporter last year: "In Pauley Perrette's case, there was an incident with the show with a dog."

Mark Harmon left NCIS viewers devastated in 2021 when it was announced that after almost two decades as the naval drama's lead, he was bowing out of the show.

At the time, he chose not to address the reasons for his exit either in an interview or via a statement, but in 2022, the Leroy Jethro Gibbs actor finally broke his silence.

Speaking in a special featurette on the show's season 19 DVD release, he said the opportunity to tackle "fresh" and "challenging" material is what kept him returning to the drama every season, alluding to the possibility that he felt that after almost two decades on the show, he no longer felt that was the case.

Following Mark's onscreen departure, showrunner Steve Binder released a statement that heavily suggested Gibbs could make a comeback in future seasons.

He said in part: "Regarding the future of Gibbs, as long-time fans of the show may have noticed over the years… never count Leroy Jethro Gibbs out."

After 13 years of playing Special Agent Anthony DiNozzo, Michael Weatherly decided to leave NCIS in 2016. 

Speaking to TV Insider at the time, he revealed that his decision had been two and half years in the making. 

Explaining how his co-star Cote de Pablo's exit had influenced his own, Michael said: "[Tony and Ziva's] great dynamic, the badinage and sparring and flirting between those two characters and how they would swing from siblings to near lovers and back to buddies, that was gone. Then I got to the point where I felt I'd stayed at the party for too long."

A devoted father, Michael also attributed his departure to a desire to spend more time with his children. 

In a 2016 interview with People, he admitted: "I think a lot about the kids and the time I get to spend with them now, at this age of four and two-and-a-half, which is such a critical time."

Cote De Pablo joined the NCIS franchise in season three as Special Agent Ziva David and stayed with the show for more than eight years before her departure in 2013.

Cote didn't immediately reveal why she quit the show, but in 2016 she opened up about her decision and said she didn't like the plans they had for her character. 

She explained: "Unfortunately because of political things and scripts not being good enough, I chose not to [return to NCIS].

"Look, I love this character! I worked for eight years crafting Ziva and when I felt like the character wasn't being treated with the respect she deserved."

She added: "They were going to send [Ziva] back to Israel and make her an unfortunate, miserable woman. I didn't think it was fair. I told them until someone can write something really fantastic for Ziva I won't come back."

CBS executives insisted they didn't want to see her go but added that it was "her decision," to end her run on NCIS. Despite her initial statement, Cote did return to the show in seasons 16 and 17 and later clarified that what she had initially said wasn't exactly correct.

She told USA Today in 2019: "I think that was taken out of context at a certain point… But I didn't leave because I wanted to go or because I was ready or because I was tired. I didn't really have an option." 

Sasha Alexander was one of the original NCIS cast members and played Special Agent Caitlin 'Kate' Todd in season one. The actress surprised fans by departing after just two seasons and 49 episodes.

In a 2012 interview with TV Guide, Sasha revealed why she wanted to exit NCIS. "People don't realize that on a network show, you make 24 episodes a year — that's 10½ months a year, 17 hours a day. It's hardcore," she said. 

"Plus, people really loved the character, and the way they did it was really shocking...it was a bullet to the head, you know?"

Asked if she had any regrets about leaving NCIS, the actress replied: "I really firmly believe in my heart that I would not be where I am today — happily married, with two kids, doing things creatively that I want — if I had stayed. I didn't want to wake up and be in my forties and go, 'Oh, my gosh!' But people don't understand."