The streets of Philadelphia looked a little different Saturday afternoon.

Some were filled with nearly naked runners as they took time out of their holiday weekend to benefit the Children’s Tumor Foundation.

Cupid's Undie Run, which takes place in cities across America each February, was created to aid neurofibromatosis (NF), a rare genetic disorder. The 1-mile fun run encourages participants to wear just their underwear — despite the cold weather in many participating cities —  though it's not required. A party/awards ceremony also proceeds the run.

The annual and normally chilly event was unusually comfortable for the underwear clad runners, as highs reached the 60s.