"Biggest Mistake" is a song by the English rock band the Rolling Stones from their 2005 album A Bigger Bang.

Credited to Mick Jagger and Keith Richards, the track is a pop song with a strongly acoustic guitar-based arrangement and lyrics, that tell the story of an older man who falls in love but then walks out on his partner.

It could be about the failed relationship between Jagger and model Jerry Hall.

Beginning in late July, the song received extensive radio airplay, particularly on BBC Radio 2, where it remained on the A-Playlist for four weeks.

Credits adapted from album liner notes.