The serial killer was taken from Saughton jail, formally known as HMP Edinburgh, to the city’s Royal Infirmary on Wednesday.
The 75-year-old was also treated at the hospital after collapsing in his cell in January.
He is serving a life sentence for raping and murdering Polish student Angelika Kluk, 23, and hiding her body in an underfloor storage the floor of a Glasgow church in 2006.
Tobin was also handed life terms for the murders of 15-year-old schoolgirl Vicky Hamilton, of Redding, near Falkirk, in 1991, and 18-year-old Dinah McNicol, from Chelmsford, the same year. He picked the student up as she hitchhiked home from a music festival.
Their bodies were found 17 years later, buried in the garden of his former home in Margate, Kent. Vicky Hamilton’s remains had been stored in Tobin’s former home in Bathgate – where he had abducted her as she waited for a bus home – and were cut in half.
The Scottish Prison Service does not as a matter of policy comment on any individual inmates.
A source confirmed Tobin, whose health has been ‘frail’ for a number of years, had been taken ill and was removed by ambulance from Saughton.
Tobin has been treated in hospital a number of times in recent years, including in February 2016 when he was taken to the city’s Royal Infirmary by ambulance after he reportedly collapsed in his cell.
He is still suspected of a number of unsolved murders including that of Jessie Earl, 22, whose body was discovered in undergrowth near Beachy Head in 1989, nine years after she disappeared from her Eastbourne bedsit.
A coroner is currently considering whether the Sussex art student Jessie Earl was unlawfully killed and DNA tests are to be carried out to see if her death can be linked to any suspect.
Tobin has consistently refused to tell detectives if he claimed any other victims during his time at large where he raped and murdered at least three young women.