BSB released their self-titled album on Aug. 12, 1997. On Saturday, the singers -- who will return to their Vegas residency in November -- were among the opening acts for Florida Georgia Line and performed at Wrigley Field in Chicago, Illinois.
McLean took to Instagram Stories to thank fans for their constant dedication to the group.
"I think it's pretty awesome that today, 20 years ago, our first U.S. album was released and here we are now, 20 years later, selling out Wrigley Field. God bless you guys," he said.
"I want to thank you guys for helping us create this 20th anniversary for Backstreet’s first album," Dorough added on Instagram. "You guys are the heart and soul of the group. You guys are the Backstreet army and happy anniversary to you too."
Earlier this year, ET spoke with BSB about their surprising secret to staying in harmony for more than two decades.
"It's like a marriage," Richardson confessed, with his bandmates quickly echoing the sentiment.
"We go to counseling," Carter added, revealing that it was Dorough who came up with the idea. "We talk things out," he explained.