Registration for the Shamrock Shuffle 8K closed Friday after reaching its capacity of 40,000 participants, officials said.
The annual race, now in its 34th year, is the world's largest road race and a sign of the start of the outdoor running season. Registration opened Dec. 3, 2012.
"The Bank of America Shamrock Shuffle 8K is a Chicago tradition that is circled on the calendars of runners of all levels, from Olympians to first-timers," Executive Race Director Carey Pinkowski said in a statement.
A limited number of spots into the sold-out event are remained available Friday through the Bank of America Shamrock Shuffle 8K Charity Program. Interested runners can sign up through any of 21 affiliated nonprofit organizations.
A two-day Bank of America Shamrock Shuffle Health & Fitness Expo will be held at Navy Pier on April 5 and April 6. The event is free and open to the public.
The Shamrock Shuffle kicks off Apr. 7 at 8:30 a.m., starting and finishing in Grant Park.