Cassidy is being treated at a Fort Lauderdale, Florida, area hospital, longtime publicist Jo-Ann Geffen told CNN on Saturday.
It is unclear what is causing his organs to shut down.
Susan Dey, Suzanne Crough, Brian Forster, David Cassidy, Danny Bonaduce, Shirley Jones, Dave Madden as "The Partridge Family". Cassidy, who played Keith Partridge on the show, captured the spirit of 1970s youth.More news: Airbus just inked its biggest airplane order ever
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Cassidy, 67, is suffering from kidney and liver failure.
Cassidy revealed his dementia diagnosis earlier this year.
The sitcom ran from 1970 to 1974 and produced a number of hit songs in real life, including "I Think I Love You", which reached No. 1 on the Billboard chart in November 1970. He's had a rocky time during the last several years, having been arrested for driving under the influence in 2010, 2013 and 2014, and filing for bankruptcy in 2015.