An 11-year-old boy was sexually assaulted as he walked along a country lane in the afternoon, according to police.
Thames Valley Police said the attack by a man believed to be in his 40s happened around 4.40pm yesterday in Wendover, Buckinghamshire.
The schoolboy was walking along Bacombe Lane, close to a bridleway, when the man approached him.
He was sexually assaulted before being able to run away.
Detective Inspector Ben Gasson said: "I am appealing for anyone who saw a man matching the description or anyone seen acting suspiciously in this area to contact police.
"The victim was not hurt during the incident but has understandably been left shaken.
"Incidents of this nature are extremely rare and are investigated thoroughly however if anyone has any concerns they can call their local neighbourhood team via our non-emergency number 101."
Neighbourhood patrols are taking place in the area and enquires are ongoing.
The offender is described as a white man aged approximately 40, with stubble on his face. He was wearing a grey and black diamond-patterned hooded top, dark blue jeans and black shoes.