"Baby, What a Big Surprise" is a ballad written by Chicago's then bassist/singer Peter Cetera, which appeared on their album Chicago XI (1977), with Cetera singing lead vocals.

The first single released from the album reached number 4 on the US Billboard Hot 100 chart.

[2] Carl Wilson of The Beach Boys and Cetera's brother, Tim Cetera, provided additional backing vocals on the recording while saxophonist Walt Parazaider plays flute on the distinctive introduction and trumpeter Lee Loughnane plays a piccolo trumpet.

Cash Box said that "frequent repetition drives the memorable chorus home, while classically influenced strings, brass and vocals lend a stately touch.

"[3] Record World said that "the interesting structure and chorus hook" explain why the song was a popular song on pop music radio stations even before it was released as a single.