Police said a 22-year-old woman was attacked while walking through an alley in the 3500 block of North Halsted around 4:30 p.m. Monday.
The victim was transported to Advocate Illinois Masonic Medical Center in stable condition.
Police described the attacker as a man between 25-32 years old, 5'5" and wearing a black skullcap, blue jeans and white gym shoes. Police say he ran away after the attack and is still at large.
Investigators urge anyone with information on the attack to contact Chicago police.