More than 300,000 attempts were made to access pornographic websites at the Houses of Parliament in the past year, official records suggest.
It is unclear whether MPs, peers or other staff are responsible, House of Commons officials said.
The figures were not all "purposeful requests" and may have been exaggerated by third-party software and websites that reload themselves, they added.
About 5,000 people work on the parliamentary estate.
The data was released following a Freedom of Information request by Huffington Post UK, which published the story with the headline Oh Yes, Minister!
However, the figures vary wildly: in November, there were 114,844 attempts to access websites classed as pornographic, but just 15 in February.
A Commons spokeswoman said: "We do not consider the data to provide an accurate representation of the number of purposeful requests made by network users."
This was because there was a "variety of ways in which websites can be designed to act, react and interact and due to the potential operation of third party software," she said.
Some of the hits may have been registered by websites that generate a number of views during a single visit, or those that automatically link to other sites via pop-ups, she explained.
Prime Minister David Cameron announced in July that most households in the UK would have pornography blocked by their internet provider unless they chose to receive it.
Online pornography was "corroding childhood" and "distorting" children's understanding of sex and relationships, he argued.
The UK's biggest internet service providers have agreed to the filters scheme meaning it should cover 95% of homes.
But one of Mr Cameron's advisers, Wikipedia co-founder Jimmy Wales, said the plans were "absolutely ridiculous".