The couple were greeted with full military and ceremonial honours, and a 19-gun salute, while the British national anthem was played.
And while the British leader's wife charmed with her style it was Barack Obama who really won over his guests with his welcome speech.
He joked that Downing Street aides told him Mr Cameron had decided to fit a basketball hoop at No 10 after their evening at a game in Ohio.
And he was "delighted" that Samantha had chosen to go to the US for her first official foreign trip.
The US leader added that the visit was one of the few for which he didn't need a translator, before drawing laughter from the crowds with his series of typically British phrases.
"We Americans and Brits speak the same language most of the time, so let me just say, David, we are chuffed to bits that you are here," he said.
"I'm looking forward to a great natter. I'm confident that we are going to keep the relationship between our two great nations absolutely top-notch."
For his part, the British PM said he'd added some words to his vocabulary after their trip to the basketball the previous evening.
He said: "I will leave America with some new words – alley-oops, brackets, fast breaks – and, who knows, that hoop may be installed in Downing Street after all."
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