A woman was sexually assaulted on a train to Inverurie from Aberdeen.
British Transport Police said the incident happened on Saturday 1 April on the 20:55 service at about 21:00.
The suspect - who got off the train at Inverurie - inappropriately touched the victim.
He was described as white, aged in his 60s, wearing casual clothes. He was thought to have been travelling with three other men and four women. BTP can be contacted on 0800 40 50 40.
Or information can be sent by text to 61016, quoting reference number 183 11/04/17.