Islam Times: Sultan was on a visit to the United States for medical tests when he died.
"With deep sorrow and sadness ... King Abdullah bin Abdulaziz mourns the death of his brother and his Crown Prince Sultan who died at dawn this morning Saturday outside the kingdom following an illness," the Saudi state press agency said.
Saudi state television said Sultan's funeral would be held on Monday.
Analysts believed he had been suffering from a form of dementia, and a March 2009 US diplomatic cable released by WikiLeaks said he was "for all intents and purposes incapacitated".
He received a diagnosis of colon cancer in 2004.
With Sultan's death, his brother Prince Nayef bin Abdul-Aziz, the longtime minister of interior, becomes next in line to rule after King Abdullah.
Sultan's official birthday in the kingdom is January 5, 1928, but some Western analysts believe he was actually born in 1924.