Police are appealing for witnesses after a concrete block was thrown over a fence on to people in a pub smoking area.
The incident happened at the Brook and Barter, in Market Square, St Neots, in the early hours of June 2.
The block struck a woman in the face and she received treatment at Hinchingbrooke Hospital for serious but not life threatening injuries.
It is believed the suspect had been drinking in the in the pub that night but had been thrown out following an argument with other customers.
DC Jennifer Park said: "This unprovoked attack caused serious injury to the victim, and had the potential to take her life. It goes without saying that throwing concrete blocks in a public space is a dangerous and stupid thing to do.
"I urge anyone with information to get in contact with us."
Anyone with information is urged to call 101 quoting incident number 35/38075/19.