The move comes just over a week after a group of state attorneys general said there weren't enough protections against blocking potentially illegal ads promoting prostitution. It's not clear if the closure is permanent, and it appears to only affect ads in the United States.
The listings came under new scrutiny after the jailhouse suicide last month of a former medical student who was awaiting trial in the killing of a masseuse he met through Craigslist, a popular site that lets users post classified ads, often for free.
Craigslist's adult services section carried ads for everything from personal massages to a night's companionship, which critics say veered into prostitution.
Craigslist CEO Jim Buckmaster said in a May blog posting that the company's ads were no worse than those published by the alternative newspaper chain Village Voice Media. He cited one explicit ad which included the phrase: "anything goes $90."
Craigslist has been caught for years in a murky legal fight that centers on how much responsibility the company bears for its ads, said Jonathan Zittrain, professor of law and computer science at Harvard University.
Prosecutors can argue Craigslist is an "intermediary" to the crime of prostitution, Zittrain said, but such cases are hard to prove. He said prosecutors must essentially prove that Craigslist knew an ad was a solicitation for prostitution; ads on Craigslist are typically worded more vaguely.
Nonetheless, to avoid a legal showdown, the company has tried to keep "inappropriate activity" off its site by screening ads.
It's unclear if Craigslist felt the attorneys general had a good argument, or if it simply got tired of spending time on the issue. But saying adult services were "censored" rather than just removing could be seen as a message to prosecutors, Zittrain said.
"They don't like being pushed around" Zittrain said.
Like many other online forums, Craigslist typically does not review ads before they are posted by users. But in 2008, under pressure from 40 state attorneys general, Craigslist began requiring posters to provide a working phone number and pay a fee for placing an ad in what is now the adult services section. Several months later, Craigslist adopted a manual screening process in which postings are reviewed before publishing.
U.S. courts have repeatedly ruled that online service providers such as Craigslist aren't liable for postings made by their users, but because Craigslist now reviews those ads ahead of time, an argument could be made that the site is playing a more active role in the postings.
State officials believe Craigslist is still not doing enough to stop illegal ads from appearing. The company did not comment Saturday.
Connecticut Attorney General Richard Blumenthal, one of the 17 attorneys general who pressed for the change, said in a statement that he welcomed the change and was trying to verify Craigslist's official policy going forward.
In an Aug. 24 letter, the state attorneys general said Craigslist should remove the section because it couldn't adequately block potentially illegal ads promoting prostitution and child trafficking.
Authorities point to the case of 24-year-old Philip Markoff as a prime example of the dangers posed by Craigslist services. The former medical student was accused of killing a masseuse he met through the hugely popular classified advertising site, which was founded by Craig Newmark. Markoff committed suicide in the Boston jail where he was awaiting trial.
If Craigslist has left the adult services business for good, it won't likely diminish the online market for sex acts, said Steve Jones, a professor of communication at the University of Illinois in Chicago who has studied Internet culture.
The business will likely shift to other adult sites, perhaps based outside the United States. "I bet there are people today who are registering domain names and saying: 'Business opportunity for me,"' he said.