The 28-year-old singer appeared in the picture with only a pair of underwear, her hair and a strategically-placed laptop to protect her modesty.
The revealing photo did not amuse some of Allen's fans -- one follower in particular wrote, "If Lily Allen is going to post pictures like that, she needs to stop using Instagram, and get a Facebook. It's obscene. Kids use Instagram, and they do not want to see that!"
Others praised the picture as a a celebration of body confidence -- Allen has lost a significant amount of weight since she gave birth to daughter Marnie Rose last year.
Marnie Rose is the singer's second child with husband Sam Cooper. The couple have one other daughter, Ethel Mary, who was born in 2011.
Allen had announced her retirement from music in September 2009, but returned and released her album The Truth About Love in September 2012. The singer plans to release her new album, Sheezus, on May 5 of this year.