The 51st Street station on the IRT Lexington Avenue Line opened on July 17, 1918. It is a local station with two local tracks and two side platforms. The two express tracks, used by the 4 and 5 trains during daytime hours, pass through a lower level and are not visible from the platforms.
The station features modern beige bricks over the original tiles, but the standard IRT-style mosaics remain intact. There is a crossunder at the extreme north end of the platforms with an elevator on each side and an escalator on the Brooklyn Bridge-bound side.