Convicted double murderer Matthew Wales was given elective surgery to treat varicose veins ahead of thousands of Victorians on hospital waiting lists, the state opposition says.

But the head of Victoria's prison system said the surgery was to correct a longstanding and painful medical condition and claims Wales received preferential treatment were "absurd".

In April 2003, Wales was jailed for a maximum of 30 years with a non-parole term of 24 years for the murders of his mother Margaret Wales-King, 68, and her husband Paul King, 75, on April 4, 2002 in a case that became known as the Society Murders.

"In the context of literally thousands and thousands of people waiting on the state's hospital waiting lists, it's obscene that a recently convicted double murderer can be afforded preferential treatment above thousands of Victorians awaiting elective surgery at public hospitals," Mr Dalla-Riva said.

But Corrections Victoria Commissioner Kelvin Anderson said a surgeon had assessed Wales' surgery was necessary to correct a "longstanding, persistent and painful" condition.

While he conceded Wales might have had surgery before Victorians on waiting lists at other hospitals, Mr Anderson said Wales waited 1,014 days for surgery, compared with the state average of 352 days.

"People on elective surgery now get speedier treatment and treatment three times (faster) than that prisoner got in this case, so in fact the real position here is the wait was longer."

Wales, now 37, invited his mother and stepfather to dinner at his Glen Iris house on April 4, 2002, then laced their soup with prescription drugs to make them drowsy.

Wales was convicted of the murders. His wife, Maritza Wales, was given a suspended two year jail term for attempting to pervert the course of justice.

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