Aetna's CEO gave a harshly critical review Monday of the federal government's Obamacare marketplace, saying, "There's so much wrong, you just don't know what's broken until you get a lot more of it fixed."

Asked on CNBC's "Squawk Box" if he knew that the rollout of Healthcare.gov would be problematic, the insurer's CEO, Mark Bertolini, said his giant company's role as an alpha tester for the system gave it a sense of how many problems the health insurance marketplace faced on the eve of its launch.

"We were pretty nervous as we got further along," Bertolini said. "As they started missing deadlines, we were pretty convinced it was going to be a difficult launch."

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His fears have been realized, he said, and the technological debacle seen at Healthcare.gov is one similar to just the handful he's witnessed in his career.

"It's nothing you ever like to repeat," Bertolini said. "Because it's very difficult. I've been there. It's career-ending in a lot of cases."

'On the fly'

"It's all been on the fly," Bertolini said of the construction of the marketplace and the integration of insurers such as Aetna, whose plans are being offered to up 40 million customers.

"We didn't get code drops until the last month before the system went live," he said.

Healthcare.gov was besieged by visitors went it went live Oct. 1 and has struggled to deal with a raft of software problems, including transmitting data to insurers and even allowing people to shop for plans.

(Read more: Obamacare overhaul)



It is not clear how many—or how few—people have even enrolled in plans sold on the site.

Asked how long the marketplace, also known as an exchange, will take to fix, Bertolini said, "That's the big question."