At a dinner in Vienna in September 2004 - a few months before the Orange Revolution swept him to power - somebody fed him a near-lethal dose of dioxin.
He no longer has visible scars.
But the 59-year-old politician told EUobserver in Brussels on Wednesday (5 June) that traces of the toxin still cause painful skin inflammations and that it has permanently damaged nerves in his legs.
He said his would-be assassins were linked to Russia.
"We all know who was serving the food at that dinner - they are in Russia right now," he said.
Speaking some 10 years after the dramatic events, he warned that Russia still poses a threat to Ukraine.
He accused Moscow of trying to "isolate" Kiev in Europe.
"It is turning Ukraine into Belarus II and it is turning Yanukovych into Lukashenko II," he noted, referring to Ukraine's current leader Viktor Yanukovych and Belarusian President Alexander Lukashenko, Putin's autocratic ally.
He said Russia's "roadmap" for Ukraine has advanced in leaps and bounds over the past few years.
It first signed a cripplingly expensive gas supply contract.
It then persuaded Yanukovych to let its navy stay in Ukraine for another 25 years and to abandon NATO membership plans in return for a gas discount.
It is now lobbying him to join the Russia-led "Eurasian Union," a new trade body, in a development that would destroy prospects of EU-Ukraine integration.
For its part, the EU has spent the time in technical talks on a political association and free trade pact.
It has also boycotted and damned Yanukovych for jailing opposition leaders, harassing media and rigging votes.
"Russia's plans are coming true 100 percent and to a large extent this is because we don't have a strong relationship with the European Union … If we don't have a dialogue with the EU, or if we have a weak dialogue, this is what makes [Russian leader] Putin so successful," Yushchenko said.
Yushchenko retired from public life after losing in 2010 elections.
But he recently created an NGO - the Institute of President Viktor Yushchenko - to promote EU-Ukraine ties.
Looking to an EU summit with ex-Soviet states in Vilnius in November, he said he will do "everything possible" to see EU leaders sign the political and trade treaty.
He described the pact in historic terms.
"During the 20th century, we declared independence six times and lost it five times … Our most important achievement in the past 21 years was to achieve independence once again. If we can get Ukraine into the family of European nations, this would be the second most important," he said.
"This course is a guarantee of our national sovereignty," he noted.
For their part, EU diplomats increasingly doubt if Ukraine will fulfil its reform demands in time to sign at Vilnius.
They also doubt whether Yanukovych really wants to do it.
The status quo has enabled him and his oligarch allies to grow rich and to build a power base that could last a generation or more.
But if he is toppled in an EU-model democratic vote, he risks losing everything.
Yushchenko, who knows Ukraine's big men up close, said the EU should exploit the ruling elite's mistrust of Russia.
"I don't think the current Ukrainian leadership is interested in becoming Belarus II," he said.
"I don't know any Ukrainian oligarch who sends their children to study in Moscow … All their kids go to schools in Europe or in the US. They have residences in Europe, in London, Brussels, in Spain, Italy, or in the US. They have business assets in Europe, in the US, all over the world, but not Russia," he noted.
"Don't you think the EU can motivate them to take the right path?" he added.
He described Yanukovych's authoritarian methods as a "darkness in our lives."
When asked if the EU should sign in Vilnius even if former prime minister Yulia Tymoshenko, Yanukovych's main opponent, is still in prison, Yushchenko said "it is time to think of 46 million Ukrainian people" instead of one woman's fate.
Yushchenko's line - that geopolitics is more important than EU values - is eerily similar to Yanukovych's own rhetoric.
Yushchenko lost power in 2010 in part due to corruption allegations.
His return to the public stage to promote EU ties despite Yanukovych's sins has prompted suspicion he is part of the Yanukovych PR machine.
"I wonder who is paying him to say these things," one EU diplomat noted.
When EUobserver asked if Ukrainian politics has made him rich, Yushchenko said:
"As of 1 January , I remember having less than $1 million in my bank account."
"I say these things because I am very deeply concerned and I am being extremely sincere," he added.
"No one paid me," he said.
Source: EU Observer