Officials are wondering what's caused this huge spike in reports of sexual assaults. They're not sure if there's been an actual increase in attacks, or if women are feeling more comfortable in reporting rapes to police and friends.
U.C. student Jessi Sosnovkaya says she knows what often leads to the sexual assaults. She's been to those off campus parties.
"You give a girl one drink, you give her another drink, you stuff something in her third drink, she's wearing a short skirt and that gives you permission to stick your hand up here skirt. I don't know, but that's how it often is," Sosnovkaya said.
Berkeley police say the increase from 20 rapes in 2011 to 39 in 2012 involved exactly that -- drugs or alcohol and someone the victim knew.
Police say the majority of the attacks did not occur on campus, but at parties in the surrounding neighborhoods. That's where an estimated 35,000 students like Brianna O'Leary live.
"It's definitely disturbing that I personally cannot feel safe in this community all the time," O'Leary said. "And that is a very realistic threat."
Berkeley Police Captain Andrew Greenwood released the latest figures this week. He's concerned because it's the highest increase in five years.
"We're very concerned because it looks like the vast majority of these reported sexual assaults are committed by acquaintances or from former dating relationships," Greenwood said.
He notes that stranger rapes in Berkeley have been extremely rare. The increase in reports of sexual assaults may be due to a campus program which encourages friends of victims to report attacks.
Greenwood says he's keeping a close eye on the numbers, "It's hard to say whether or not it's the beginning of a trend or an outlier year in terms of the high number of assaults, and we'll be tracking that very carefully as well."
According to Greenwood, many of these attacks are unreported. Berkeley police say they are working with U.C. police on rape prevention and education about reporting.
U.C. police investigated two rapes in 2011 and two in 2012. U.C. Berkeley officials were not available for comment.