Human Rights Watch (HRW) interviewed more than 50 North Koreans who fled the country in the last seven years and published their findings earlier this week.
The women said they suffered rape, assault, sexual harassment, verbal abuse and intimidation at the hands of North Korean police and other officials.
One woman said it was so commonplace she did not think being abused was unusual.
Responding to the report, North Korea's association for human rights studies branded the women interviewed as "human scum".
The association called the report "preposterous" and claimed it was "a part of [a] political scheme fabricated by the hostile forces ... to tarnish the image of the DPRK", the country's official acronym, according to the state Korean Central News Agency.
"It is also an extremely dangerous provocation aimed at reversing the tide of peace and prosperity on the Korean peninsula," the statement said.
The 86-page report concludes that unwanted sexual contact and violence is so common in North Korea it has come to be accepted as part of ordinary life.
It reads: "While sexual and gender-based violence is of concern everywhere, growing evidence suggests it is endemic in North Korea."
The US-based rights group's report included testimony from an anonymous former textile trader in her 40s, who recounted being treated like a sex toy "at the mercy of men".
"On the days they felt like it, market guards or police officials could ask me to follow them to an empty room outside the market, or some other place they'd pick," where they forced sexual encounters, she said.
"It happens so often nobody thinks it is a big deal. We don't even realise when we are upset," she added.
Another trader said: "They consider us [sex] toys. We [women] are at the mercy of men."
She continued: "Sometimes, out of nowhere, you cry at night and don’t know why."
Those interviewed all left the country after 2011, when the current leader, Kim Jong Un, rose to power.
In a summary of the report, HRW said: "The government fails to investigate and prosecute complaints, or to provide protection and services to victims, and even asserts that the country is implausibly free of sexism or sexual violence."
"Sexual violence in North Korea is an open, unaddressed, and widely tolerated secret," said HRW executive director Kenneth Roth.
