The world around cryptocurrency is great, but investors should be a little more careful and know the risks, CNBC's Jim Cramer said Tuesday.

"I'm not denying the crypto world, I'm supporting the crypto world. I think that crypto is great," Cramer said on "Squawk Box." "But I think we have to be a little more careful."

Bitcoin futures began trading on the Cboe last week, and the CME, the world's largest futures exchange, launched its own bitcoin futures contract on Sunday.

Cramer said he believes there are companies that are "taking advantage of the enthusiasm" around digital currencies, especially bitcoin.

"When you see that level of enthusiasm, what that says is that there are true believers and you can't talk a true believer out it. And I always say, 'Look, as long as you know the risk, be my guest,'" he said.

"I never, ever mind anybody trying to make money," Cramer said. "I've had people come on these shows saying they missed it. I am not one of those. I'm saying as long as you know the risk, it's fine."

"Selling bitcoin is like you're defacing the flag," Cramer later said on "Squawk on the Street." "There's like this patriotic urge to not sell bitcoin."

Earlier this month, Cramer said the launch of bitcoin futures on the Cboe was a "very big victory" for the digital currency.

But in the early days of the cryptocraze, Cramer was also warning about the risk — at one point comparing it to "'Monopoly money.'"