Russian prison officials have launched an investigation into the alleged abuse of inmates rights at a prison hospital in St Petersburg.
Most of the inmates are infected with HIV, hepatitis or tuberculosis.
They say they are denied the proper treatment guaranteed by law.
The inquiry comes after letters from the prisoners to a human rights group were made public. More than 30 people died at the hospital in the first six months of this year.
The letter says there was a spate of deaths in the spring, after prisoners admitted to the hospital with pneumonia were left without care.
One of the inmates who contacted the lawyers has since died.
Another prisoner, Eduard Razin, who suffers from HIV, hepatitis and TB, wrote: "I haven't received proper treatment from the day I was moved to the prison.
"All I am given is one injection a day for high fever, and chemotherapy for TB. When I ask for more injections for fever the nurses say that hasn't been prescribed and they say I will die soon."
The human rights group Agora says the prisoners who have decided to speak out are being punished.
Razin is being transferred to another prison in Karelia, in the North of Russia. The prison is notorious for its mistreatment of infected inmates.
Lawyers say that Razin saw his internal prison papers, and is described there as healthy and capable of travel without any medical assistance.
Another prisoner says he receives no retro-viral drugs despite having a dangerously low immune level. "I complained and, as a punishment, was sent to a prison colony for TB-infected," he says. "But the colony refused to take me as I was too ill."
Dmitry Dinze, the lawyer who spoke to some of the prisoners, says his organisation has long suspected that patients in the Gaaza prison hospital were denied treatment. He says though it could not verify this, as the prison service declines to give out any information on the state of its prisons.
The BBC asked the prison authorities to provide official death statistics. A prison major, who declined to give his name said: "Which period are you looking into? They peg out daily."
The Russian federal prison service says it will not comment until the official investigation is complete. However, a representative of the service suggested to the BBC that mortality rates in the prison hospital were normal for a clinic with such gravely ill patients.
The scandal comes in the wake of numerous reports of prison abuse in Russia. One of the more prominent cases was the death in 2009 of Sergei Magnitsky, a lawyer working for a US firm.
In 2010, in an attempt to provide independent medical care, the federal prison service ruled that medical staff working in jails were not subordinate to the prison authorities. But this change meant a different financial structure, and the salaries of prison doctors were cut.
According to Vladimir Shnitke, the head of St Petersburg's public watchdog for prisons, this forced many doctors to leave the Gaaza hospital, and may explain the alleged inadequate level of treatment.
Mr Shnitke, quoted by The Moscow News daily, says he will be pressing for a criminal investigation of possible cases of medical negligence in the hospital.