More than 20 women have been victims of sexual assaults on trains and at railway stations in South Yorkshire and North Derbyshire in the past five years, The Star can reveal.
British Transport Police said there have been 21 reported offences in the region.
Some 11 of the assaults were reported in Sheffield, with three in 2013 alone.
Six assaults took place in Doncaster and two at Meadowhall, with single incidents also reported in Rotherham and Chesterfield.
Nationally, there was an increase in reported incidents between 2012 and 2013.
Last year, 576 offences were reported - up on 483 reported the year before.
In the past five years, more than 2,500 sexual assaults have been carried out against women on trains nationally.
British Transport Police today said the actual number of assaults in Sheffield and surrounding areas is likely to be higher than the official figures.
Chief Inspector Graham Bamford, who is responsible for the South Yorkshire region for British Transport Police, said that while 21 reported offences was ‘clearly too many’, the figures represent one offence for every 3.7 million passengers who have used trains in the area in the last five years.
He added: “Of course, this does not mean we should be complacent and, when offences are reported, we work closely with local police forces and the train companies to gather all possible evidence and to trace offenders as soon as possible.
“Sexual offences are particularly distressing for the victims and we have procedures in place to ensure they are fully supported from the first report through to the conclusion of any criminal proceedings.
“We are aware there is still a degree of stigma attached to sexual offences, and a level of under-reporting, but I want to assure all victims that we take all reports seriously. I urge anyone who has been subjected to unwanted sexual behaviour to get in touch.”