The four-vehicle collision was reported at 9:30 p.m. near Mulholland Drive, according to the Los Angeles Fire Department.
A man and a woman were taken to the hospital by paramedic ambulance, and a woman was transported with injuries that were not life-threatening, the Fire Department said in a statement. A boy "is being signed out on scene and will not be transported," the news release said.
The cause of the crash was not immediately known.
Southbound traffic was backed up for miles after the pileup forced the shutdown of all but one southbound lane at the scene.