An MPAA spokeswoman said Valenti, 85, suffered the stroke "recently," CNN said Tuesday.
"He is under a doctor's care; he is resting comfortably," the spokeswoman said.
A spokeswoman for Johns Hopkins Medical Center confirmed that Valenti is a patient, adding, "The family doesn't want us to give out any information."
Valenti's agency, Weekley & Valenti, handled the media matters during the Nov. 22, 1963, visit of President John Kennedy and Vice President Lyndon Johnson to Dallas. Valenti was six cars behind the president's in the motorcade when Kennedy was assassinated.
Three years later, Valenti became president and chief executive officer of the MPAA, which he led until 2004, when he resigned. Valenti was a central figure in creating the movie rating system -- now G, PG, PG-13, R and NC-17 -- as a way to rate films as appropriate for certain age groups.