The Nielsen ratings company says nearly 18.5 million viewers tuned to Thursday night's live telecast of the Rodgers and Hammerstein musical.
Although a preliminary audience average, NBC says the figure is expected to hold up as a measure of the three-hour production's viewership.
"The Sound of Music Live!" starred Carrie Underwood in the role of Maria. Stephen Moyer, of HBO's "True Blood", played Capt. Von Trapp.
It was the first full-scale musical staged live for television in more than a half-century.