Amid speculation that Trump would refuse to meet the Ukrainian leader, Poroshenko had what the White House described as a "drop-in" with the US president.
"We've had some very, very good discussions," Trump said as the pair sat side-by-side in the Oval Office.
"I think a lot of progress has been made," Trump added, saying it was a "great honor" to host Poroshenko.
Trump did not touch on the thorny details of the relationship.
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The crisis has left 10,000 dead and heightened tensions between the West and the Kremlin, which considers Ukraine inside its "sphere of influence."
Ukrainian officials have long been frustrated by Washington's refusal to provide lethal weapons and its insistence on linking financial help to deep economic reforms.
But that concern has intensified since the election of Trump, who has often appeared reluctant to put pressure on Russian President Vladimir Putin to solve the crisis.
Last week, Secretary of State Rex Tillerson raised eyebrows by suggesting that the United States should not be "handcuffed" by an international plan to end the crisis.
Despite the lack of substance, Poroshenko will likely see the meeting as a victory.