The event, where sets of triplets gather to share stories and bond, kicked off Saturday in downtown Baltimore, The Baltimore Sun reported.
Most of those who attend the event are teenagers, but some are infants and some are college-age, the report said.
"These are the only people who can actually relate to you," said Ahmad Jones, 17, of Silver Spring, Md., who attended the convention with his brothers Malik and Khalil
"We don't get to be with other triplets every day, so when it's here, it's special," said Laurel Samosa, 18. Laurel and her sisters Elizabeth and Adrianna all wore the same blue dress on Saturday.
Along with a group photo, the triplets attended workshops, such as "1+1=3," which focused on issues that come from having three kids in the same grade at school, and "Cheaper by the Dozen," on buying in bulk.