Foulk, 63, received the maximum sentence for 20 counts of forced oral copulation, nine counts of sodomy by force and two counts of lewd and lascivious acts on a child, Los Angeles County District Attorney's Office spokeswoman Shiara Davila-Morales said Wednesday afternoon.
He was convicted by a jury on Feb. 3 in Judge James Pierce's Long Beach courtroom but was acquitted of two counts of sodomy by force and two counts of forced oral copulation, Deputy District Attorney Danette Gomez said.
Gomez said the jury acquitted Foulk of those charges because by then his adopted son was over 18 and in college, and the panel did not believe the prosecution had proved beyond a reasonable doubt that duress had occurred.
The sexual abuse charges of which he was convicted began in 1992 when the victim was nine years old, and ended in 2001, Gomez said.
"I'm very pleased with the maximum term," Gomez said, noting that Judge Pierce imposed eight years consecutively on the counts. "That sends a powerful message."
Foulk was executive director of Napa State Hospital between 2007 and his arrest on Feb. 24, 2010.
After Foulk's conviction, his attorney Richard Poland said the victim, now 27, was not a credible witness.
"My client said he never touched that boy. Our defense was, it didn't happen," Poland said.
Long Beach police began investigating Foulk in September 2009. Police said at the time of his arrest that they were looking into allegations of abuse against five victims dating back to 1975.
Gomez said there were a total of 12 alleged victims, counting Foulk's adopted son, and that the molestation allegations dated back to the 1960s. The judge allowed four of them to testify against Foulk.
Those alleged crimes were not prosecuted because the statute of limitations had expired, Deputy District Attorney Lesley Klein said when Foulk was arrested last year.
Poland did not immediately return a call Wednesday afternoon for comment on the sentencing.