A driver of a white van called out to a woman who was walking with her child in a pushchair in Little Stanion before indecently exposing himself.
The flashing happened on Monday, April 29, between 1.45pm and 2.15pm between the second and third roundabouts on Long Croft Road.
The woman was walking along the road when a man next to a small white van called out to her.
He indecently exposed himself to the woman, who ran off.
A Northamptonshire Police spokeswoman said: "The suspect is described as a white man, aged between 25 and 35, of average build, with short mousey brown hair.
"He had a distinctive tattoo on the side of his neck and was wearing a blue t-shirt and dark blue cargo-style trousers.
"He drove a small white van with red writing on the side."
Witnesses or anyone with information regarding this incident should contact Northamptonshire Police on 101, or Crimestoppers anonymously on 0800 555111.