The two hated figures are thought to have been killed when US forces attacked their hideout in Mosul on Tuesday.
Uday, who commanded the Fedayeen militia, was ranked "ace of hearts" in the US army's pack of cards of 55 most wanted Iraqis, while Qusay was "ace of clubs".
Uday was perhaps the most hated figure in Iraq and narrowly escaped a 1996 assassination bid.
He was a sadist with a taste for cruelty so extreme that even his father was forced to acknowledge he would not be a worthy heir.
But although Uday symbolised the brutality of the Iraqi regime, his powers were severely curtailed.
Although he retained the privileges of the son of a dictator, he was shunted from the real centres of power by his quieter, younger brother Qusay.
It was not the life that Uday had intended. Of Saddam's two sons, he was the flamboyant one with a penchant for fast cars and loud and drunken parties, as well as murder, rape and torture.
His public duties ranged from the Iraqi Olympic Committee and the national football team, to an extensive media empire.
He also was in charge of the dreaded Saddam Fedayeen militia.
His search for public approval, in a bid to gain acceptance before taking over from his father, was behind his close interest in sport.
Footballers say he never really understood the game itself, but was desperate enough to win that he would phone up the dressing room to threaten to cut off players' legs and throw them to ravenous dogs.
Uday's excesses carried over into his private life where he had a reputation for ordering any girl or woman who caught his eye to be brought to his private pleasure dome.
His palace was decorated with indoor fountains and erotic murals in the grounds of his father's presidential estate.
A nearby chamber contained huge stashes of drugs as well as an HIV testing kit, according to US forces.
Weapons and cars were also among his passions. His Yacht Club pad was home to a dazzling collection of pistols, machine-guns and daggers.
"He had no less than one hundred cars, including 20 Rolls Royces," a source said.
But his brutality finally caught up with him in 1988 when he bludgeoned to death his father's bodyguard in front of horrified partygoers.
He also shot one of his uncles in the leg. The murder, shootings, and other erratic behaviour put him in permanent disfavour with Saddam.
Unsuitable for succession
Uday was briefly exiled to Switzerland and was never again deemed suitable for succession.
Uday's marriages were a further source of embarrassment to his father - his two brief dynastic liaisons were dissolved after Uday beat up his brides.
His removal from power became permanent in 1996 when gunmen fired on his red Porsche as it sped through the streets of Baghdad.
The attack left Uday partly paralysed and he still walked with a limp.
Uday was a notorious womaniser
The quieter brother
Before the US-led war which toppled Saddam Hussein, younger son Qusay was the heir apparent to the Iraqi strongman's throne.
Qusay was Saddam's main strategist during the war.
When he disappeared, he was at the apex of his powers, a position he attained only a few days before the start of the US attack when he was given absolute charge of four key regions.
He was also reported to have taken control of much of Iraq's finances.
According to US intelligence reports, Qusay helped himself to $1bn from the Iraqi central bank a few days before the conflict began, carting the money away in three trucks.
But while it took the threat of the regime's obliteration to put Qusay in formal charge of Baghdad, he had been quietly accumulating power for years.
Republican guard commander
Before the war he was the commander of the Republican Guard, believed to be the most elite of the Iraqi fighting units.
He also presided over a network of spies and informers in the Iraqi security services.
Unlike Saddam's first-born son, Qusay did not crave the limelight.
Little is known of his lifestyle, other than he was married to the daughter of a general and had two children.
But behind the awkward demeanour was a man as feared and as ruthless as his father. He was just more adept at hiding it than Uday.
By 1991, Saddam thought enough of his second son to put him in charge of the bloody suppression of the Shia rebellion in the south in 1991.
Later, the Americans alleged he was put in charge of hiding banned weapons from the first wave of inspectors.
In November 2001, the Tehran-based Supreme Assembly of the Islamic Revolution in Iraq (SAIRI) claimed that Qusay survived an assassination attempt carried out by two senior security service officers.
SAIRI said that the officers tried to crash into Qusay's car as he left the presidential palace in Baghdad "then finish him off with bullets".
But Qusay "became aware of the pair's intention at the last minute after seeing their car speed toward his", SAIRI said.
It had appeared clear that Saddam was grooming his elder brother Uday to take over one day.
But after the assassination bid against Uday in 1996, the Arab press reported that Qusay had his father's preference, despite official denials of any power struggles.
However, despite being rivals in life Uday and Qusay went on the run and, it seems, died together.