A man indecently exposed himself to a woman who was walking along an alleyway between Bamburg Close and Greatfolds Road, Corby, on Wednesday afternoon.
The woman was walking along the path sometime between 1pm and 1.50pm when a man standing in the alleyway dropped his trousers and exposed himself.
He was white, in his early 20s, with very long dark hair, unkempt, wearing jeans and carrying a can of beer or lager.
Police would like to speak to anyone who may have witnessed this incident or who may recognise the description of the offender.
Witnesses, or anyone with information about this incident, are asked to contact police on 101. Alternatively, phone Crimestoppers anonymously on 0800 555 111.