The two men aren't said to be especially close, but David Cameron is about to be honoured like no other world leader before.
When President Obama came to London last year, he was allowed to flip burgers in the Downing Street garden with the PM.
But David Cameron is being treated to what you might call an upgrade on his visit: he's being allowed to fly in Air Force 1 with President Obama - the first world leader to do that.
It will surely rank as a highlight of David Cameron's visitto the US - becoming the first world leader to accompany President Obama on AirForce One.
But why exactly are they going to Ohio to watch a basketball game later?
Well, for an American president in an election year, the fact that Ohio is a swing state makes it a marvellous photo opportunity. And the Prime Minister?
Could he perhaps be accused of taking sides in US politics? Not according to his spokeswoman, who offered this explanation: "He appreciates basketball."
Clearly this visit is supposed to show the strength of the special relationship between the countries.
In a jointly-written article in the Washington Post today, the two men said:
"The alliance between the US and Great Britain is a partnership of the heart, bound by history, traditions and the values we share.
Afghanistan is likely to dominate their agenda, not least because of the killings of 16 civilians over the weekend by an American serviceman.
There was talk this morning that the withdrawal of British and American troops might be speeded up, but Downing Street have been playing that down, saying that they are sticking to the plan envisaged at a NATO meeting earlier this year.