A third of reported rapes in Tayside have gone unsolved in the last three years.
New figures, provided to the Tele via a freedom of information request, show that 762 rape reports have been recorded since 2014.
Of that figure, 253 went undetected by Tayside Police Division.
Detection rates up to December 2017 dropped to 121, down from 127 the previous financial year.
During 2016-17, there were 206 rape reports made to police, which fell to 185 the following year.
More than 40% of rape allegations in Dundee are of a historical nature, higher than the Scottish average.
Historical allegations are classed by Police Scotland as reports made more than one year after the incident took place.
The Women’s Rape and Sexual Abuse Centre in Dundee works closely with police to tackle the issue locally.
Sinead Daly, the centre’s manager, said a time lapse in reporting an incident to the police can make it difficult for officers to obtain corroborating evidence.
She told the Tele: “We are working closely with the police through our advocacy service to try to improve women’s experiences of reporting to the police and engaging with the court process.
“Such is the impact of sexual violence and the trauma that is associated with it, many women just can’t face reporting to the police in the immediate aftermath.
“Any time lapse can sometimes make it difficult for police to acquire the necessary corroborating evidence.”
Ms Daly added: “We have, however, protocols in place to enable women who have been recently sexually assaulted or raped to have forensic evidence gathered and stored anonymously. This evidence can be held for eight years, so if a survivor wishes to report it at a later stage, she can have forensic evidence to support the complaint.
“We would encourage any woman who has been raped or sexually assaulted and who is thinking about reporting it to contact us and ask for a referral to our advocacy service.
“Call 0300 3652001, or email firstname.lastname@example.org.
“We also have lots of information about the process of reporting incidents to the police on our website at wrasac.org.uk.”
A spokeswoman for the force said: “Police Scotland takes every report of sexual crime very seriously and thorough investigations are carried out.
“We will investigate all recent and historical sexual crimes and these can be complex and protracted in nature.
“Sexual crimes have a life-changing impact on the victims and we work closely with partner agencies to ensure that they receive the necessary support.
“We want to encourage people to come forward and report these crimes to us, as we know that they are under-reported.”