Doctors are being issued advice on how to handle patients who make amorous advances towards them on social media.
The Medical Defence Union (MDU) said social media meant doctors were "more accessible than ever" to patients who wanted more than just a professional relationship.
The MDU said that online advances could leave medics feeling uneasy.
And on some occasions these incidents could lead to doctors being stalked or harassed, it added.
Dr Beverley Ward, MDU's medico-legal adviser, said: "The MDU has helped around 100 members over the last five years with advice on how to deal with patients making amorous advances.
"A handful of these involved the type of stalking behaviour where a doctor may need to involve the police.
"With doctors more accessible than ever via social media, amorous approaches from patients can feel intrusive.
"If they are not nipped in the bud, or even unwittingly encouraged, things can get out of hand."
She added: "Some patients create a fantasy affair to which the doctor is completely oblivious.
"Others can be very distressed if they feel their advances are being ignored or rejected, and they can become aggressive or vindictive.
"The MDU has seen cases of doctors referred to the General Medical Council by patients alleging a fabricated sexual relationship, or even complaints to the police of sexual assault.
"We can support doctors facing this difficult situation so it's important to involve us as soon as becoming aware of a potential problem.
"By warning the patient that this type of behaviour is inappropriate and must stop, it can be possible to get the doctor/patient relationship back on a professional footing.
"Failing that, you may need to transfer the care of the patient to a colleague or even remove the patient from the practice list."
MDU advice includes keeping a log on unwanted advances and reviewing privacy settings on social media.
A case of a patient stalking his doctor prompted an MP to call for longer prison terms for stalking.
Tory backbencher Alex Chalk said he wanted the maximum sentence at least doubled from the existing five-year limit.
The Cheltenham MP said he had been inspired to act by constituent Dr Eleanor Aston, who he said had suffered "a horrific ordeal" for seven years at the hands of a former patient.
He said Dr Aston's stalker, Raymond Knight, had turned up at her surgery more than 100 times, posted "foul items" though her letterbox, followed her on patient visits, slashed her tyres and sent threatening emails.
MPs heard that after being jailed for a first time, Knight resumed his activities once he had been released, when Dr Aston received packages at home and at work.
The judge who sentenced Knight for a second time last year admitted he was dangerous, said Mr Chalk, and expressed his own frustration he could not hand Knight a longer sentence.