Justin Bieber Performs on 'Late Show With David Letterman' (VIDEO)

David Letterman seemed stunned by the Biebermania that inundated last night's 'Late Show' (weeknights, 11:35PM on CBS) to see the 16-year-old R&B sensation perform.

"Oh my God... look outside, these people waiting across the street and in the rain for Justin Bieber," Dave said as the camera panned the line outside the studio.

After Justin's number, the late-night host asked, "Is your mom pickin' you up?'

Watch his response after the jump. David Letterman seemed stunned by the Biebermania that inundated last night's 'Late Show' (weeknights, 11:35PM on CBS) to see the 16-year-old R&B sensation perform.

"Oh my God ... look outside, these people waiting across the street and in the rain for Justin Bieber," Dave said as the camera panned the line outside the studio.

After Justin's number, the late-night host asked, "Is your mom pickin' you up?'

Check out his response.