How does legendary (red) rocker Sammy Hagar recruit all-star musicians for his annual benefit concert at the Fillmore in San Francisco? "The first thing I do is go to people who owe me," the former Van Halen frontman tells Billboard of his Acoustic-4-A-Cure concert, set for May 15.

"Last year, I flew up from Cabo to play an event with Dave Grohl to support local schools and just told him ‘Ok, I’ll do this but you need to keep May 15 open for me,'" Hagar explains. "Same thing with Mick Fleetwood. I played his restaurant in Maui for charity. I’m not trying to force anyone to play -- they’re just returning the favor."

The three will be joined this year by Pat Benatar and Neil Giraldo, ex-Eagles guitarist Don Felder, guitarist Vic Johnson, Sarah McLachlan, Steve Vai and Bob Weir for an all-star acoustic jam session to raise $100,000 for pediatric cancer research at UCSF Benioff Children's Hospital. Hagar created the event three years ago with Metallica's James Hetfield after meeting Dr. Jean Nakamura, a physician and leading scientist searching for a cure to pediatric brain cancer.

"The money we raise helps her pay for assistants so she can spend more time in the lab," Hagar explains. "She's doing incredible research for infants born with brain tumors that have to be dealt with immediately. She’s trying to keep them going and has great research on building their immune systems so the kids can heal themselves."

Past events have included collaborations with Green Day's Billie Joe Armstrong, Motley Crue drummer Tommy Lee and guitar great Joe Satriani. While many of the performances are rehearsed the day prior, there have been plenty of impromptu jam sessions and well-known covers.

"This year I’m doing 'Hotel California’ with Don Felder, which is going to be nuts, plus 'World Turning' with Mick Fleetwood and Steve Vai," Hagar explains. "And I make sure we have a female every year. I asked Sarah (McLachlan) and almost immediately, boom, she's in. And once Pat Benatar found out Sarah was in, she signed on too."

Hagar says Acoustic-4-A-Cure is inspired by Neil Young’s annual Bridge School Benefit concert at the Shoreline Amphitheatre in Mountain View, Calif., as well as Hagar’s support of charities in both California and Maui, where he lives part-time.

"It just feels so good to be hands-on," he tells Billboard. "You know you can write checks all day long man but when you go down to the food bank and you hand out food that you helped buy for others, you walk away feeling pretty good. It elevates your spirit."

Tickets go on sale this Friday and cost $150 each for a general admission ticket and a commemorative t-shirt. A limited amount of VIP tickets are available at $500 each and include access to an exclusive VIP area to view the concert, an Acoustic-4-A-Cure T-shirt and poster and complimentary food and drinks. Ticket information is available at www.acoustic4acure.com.

"You're going to pay a premium price, but it’s going to be an incredible night of music and all the money's going to be given to these kids," Hagar says. "We're all doing this together. Everybody's getting to do what they want. The fans get to see a great show. We get to play for people and get way out of our element."