High school students are wearing white t-shirts and encourage classmates to remain virgins until they are married.
The conservative US Christian group Liberty Counsel, which organised the day, said US teenagers should make a "public demonstration" of purity.
A public demonstration, huh? Would that involve breaking the hymen and having the blood flow out on the soccer field?
US teenager Melissa Millis, who says she will wear a white t-shirt to promote the Day of Purity at her Michigan state school, told the Associated Press news agency she was tired of feeling pressurised.
''The way sex is talked about, it's so casual, like it's an everyday thing, like going to McDonald's," she said.
"Can I get the number 5, super sized? Oh, and I'll take a handjob from the 99 cent value menu."