NEW YORK (UPI) -- Runners in 37 U.S. cities and 12 Australian cities stripped down to their skivvies to run through the streets and raise money for cancer research.

Cupid's Undie Run, an annual event timed to coincide with Valentine's Day, took place Saturday afternoon in U.S. cities including New York, Chicago, Detroit, Cleveland, Salt Lake City, Dallas, Houston, Los Angeles, Nashville, Philadelphia, and Oklahoma City.

Twelve Australian cities, including Sydney, Melbourne, Brisbane, and Canberra, also participated in the underwear run.

The event featured participants in their underwear running a mile to raise money for the Children's Tumor Foundation, a charity dedicated to neurofibromatosis, a condition that causes tumors to grow all over the body.

Organizers did not yet offer numbers for Saturday's event, but last year's undie run raised more than $3.5 million for neurofibromatosis research.

"We are here to put the hilarity in charity and we bare because we care," Dan Frenia, organizer of the Philadelphia Cupid's Undie Run, told NJ.com.

The event's official website explains the purpose behind the nearly nude dress code.

"Why do we run with our butts out? It's simple. We run in our undies because people with NF can't cover up their tumors. They can't put clothes on to feel more comfortable, so why should we?" the website states.

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