It happened in the Merchants Square shopping center in the 4400 block of Governor Printz Boulevard in Edgemoor around 10:30 a.m.
Authorities say a man, believed to be 19 years old, fell 20 feet from a steel girder.
He was taken to the hospital by state police helicopter.
There was no immediate word on his condition, but since he was airlifted he must have been in serious condition.