In response to the Boston Marathon bombings, there will be additional security officers and police. Bags will also be inspected near the start.
The marathon will start with the top runners at the Ferry Building at 5:30 a.m. The course weaves through the city, across the Golden Gate Bridge, and back to the Embarcadero near Mission for the finish line.
Road closures will begin Saturday at midnight and remain in place through Sunday afternoon.