A man exposed himself to an 18-year-old woman in Penwortham, police said.
It happened at around 6.30pm on Sunday on Cop Lane.
The man first approached the woman on Cop Lane at the junction of Bank Parade and exposed himself.
She ignored the man and continued to walk west along Cop Lane before being confronted by the man again exposing himself at the junction with Glenway.
He is described as white, 5ft 8 t of a slim build with short shaven dark brown and grey hair, grey facial stubble and is thought to be in his late 30s.
He was wearing a distinctive navy blue work type jacket with silver high visibility markings and grey trousers.
PC Andy Fleming of Preston Police said: “This was a disturbing incident for the young woman involved and I would urge anyone who may have seen a man matching the description given in the area on Sunday evening to contact us as soon as possible.”
Anyone with information should contact police on 101 quoting log number 1196 of November 30.
Alternatively, they can contact Crimestoppers anonymously on 0800 555 111 or online at Crimestoppers-uk.org. No personal details are taken, information is not traced or recorded and you will not go to court.