Participants were encouraged to remove their outerwear whilst underground, and to act "normally"
Despite a cold snap across much of the northern world, users of public transit systems in a number of cities took off their trousers for No Pants Day.
The event, which began in New York City in 2002, sees participants with bare legs mingling with other passengers.
Organisers Improv Everywhere say 3,000 people took part in New York with more in 43 other cities in 16 countries.
The group says its mission is to cause "scenes of chaos and joy in public places".
Participants were told to meet at a designated train station fully clothed before boarding and removing their trousers.
People are urged to keep a straight face, act normally and not acknowledge other people without trousers.
'Feeling of freedom'
One of the organisers in Washington, DC, said "there's not really any point or any cause" to the event.
"We're just trying to put smiles on people's faces," Bruce Witzenburg told the Washington Post.
With temperatures hovering around freezing in Edmonton, Canada, participant Sarah Jackson said she felt liberated by the event.
"People you know look around, they're curious and interested and for some reason I feel incredibly comfortable in my underwear on the LRT," she told CTV News.
On its website, Improv Everywhere said groups from Adelaide, Australia, to Zurich, Switzerland had organised their own No Pants Subway Rides.