Aren’t Fox is preparing to launch an office in San Francisco on May 1, joining a number of firms that plan to open up shop in the city.

The firm will open the office with at least five lawyers who will be based in San Francisco full time. Four of those lawyers will be transferred from the firm’s other offices, and one has been hired from outside the firm, said partner Robert O’Brien, who will lead the office. O’Brien, who also manages the firm’s office in Los Angeles, will divide his time between Northern and Southern California along with partner Stephen Larson.

O’Brien said the firm’s decision to open up shop in San Francisco was driven by client demand. The firm already counts Disney-Pixar, F. Korbel & Bros., Qualcomm and Western Digital among its clients in the Bay Area, he noted. The office will focus on representing clients in health care, IP, commercial litigation and automotive work, he added.

“We’re not coming to San Francisco on the hope that we’ll develop work there,” he said. “We’re coming because we already have work in San Francisco.”

The firm is negotiating a lease for space in the financial district, O’Brien said.

Washington, D.C.-based Arent Fox had 315 lawyers and revenue of $230 million in 2011.

The firm is in talks with other lawyers outside the firm about joining the San Francisco office, O’Brien added. A string of lateral hires expanded the firm’s footprint in Los Angeles from about 10 lawyers when the office opened in 2006 to 72 today, he noted. The office grew further last week with the hiring of Los Angeles-based IP partner J.D. Harriman, who joined the firm from DLA Piper. Harriman said he expects the firm’s new presence in San Francisco to deepen his practice.

“I plan to be active in helping promote the office and will probably visit the office regularly to help out,” he said.

Recruiter Larry Watanabe said he expects Arent Fox to attract talent in the Bay Area as well given its track record in Los Angeles.

“They have brought laterals on board whose practices have increased since joining the firm, and I think they’ll have success in San Francisco as well,” he said.

Watanabe said he is now helping two other firms move into San Francisco and has been contacted by at least half a dozen that are interested in doing the same.