Adidas apologised for sending an insensitive email congratulating runners on "surviving" the Boston Marathon.
Runners received a promotional message from the athletic apparel company on Tuesday following their completion of the race, with the subject line reading: "Congrats, you survived the Boston Marathon!"
Monday's 121th running of the Boston Marathon was the fourth since three people were killed, including two women and an eight-year-old boy, in a bombing at the finish line in 2013.
More than 200 people were injured in what was the most lethal act of terrorism committed in the United States since the September 11 attacks in 2001.
"We are incredibly sorry," Adidas said in a statement.
"Clearly, there was no thought given to the insensitive email subject line we sent Tuesday.
"We deeply apologize for our mistake. The Boston Marathon is one of the most inspirational sporting events in the world.
"Every year we're reminded of the hope and resiliency of the running community at this event."
Kenyan runners Geoffrey Kirui and Edna Kiplagat won the men's and women's races respectively on Monday.