Foulk, 63, is suspected of molesting five boys under age 14, Long Beach police Sgt. Dina Zapalski said.
Foulk was arrested on hospital grounds early this morning on a $3.5 million warrant out of Los Angeles County alleging 35 counts of lewd and lascivious acts with a child, Long Beach police said in a news release.
Zapalski said some of the boys were molested in Long Beach between 1975 and 2004; the other alleged crimes occurred between 2004 and 2006 in Rancho Murieta, a small community in the Sierra Foothills 25 miles east of Sacramento where Foulk moved in 2004, she said.
The crimes were not connected to Foulk's employment, Zapalski said.
The Long Beach Police Department began investigating the case in September 2009 after one of the alleged victims contacted police.
Foulk is expected to return to Long Beach today to be booked into jail there, Zapalski said.
Police said the investigation is ongoing and there could be additional victims.
Foulk became director of Napa State Hospital in 2007.