A British computer expert accused of hacking into US military networks would be at real risk of psychosis or suicide if extradited to America, the High Court was told.
Gary McKinnon, 42, faces a lifetime in jail if he is found guilty in the US of sabotaging vital defence systems after the September 11 terror attacks.
But his supporters say he acted through "naivety" as a result of his Asperger's Syndrome - a form of autism - and should not be considered a criminal.
Edward Fitzgerald QC, appearing for Mr McKinnon, told the High Court his medical condition was likely to give rise to psychosis or suicide if removed to the US, far away from his family, and he should be allowed to stand trial in the UK.
The QC said: "The very fact of extradition will endanger his health."
The chances of Mr McKinnon's health being endangered were further increased by the real risk that he would be detained pre-trial in tough conditions in an American Supermax high security prison, violating Article 3 of the European Convention on Human Rights protecting against inhuman and degrading treatment.
Mr Fitzgerald accused Home Secretary Jacqui Smith of failing to inform herself and properly consider these risks before deciding in October last year to permit extradition.
He said she had also failed to request an undertaking from the US that Mr McKinnon - "a seriously disordered person" - would be repatriated to serve his sentence in the UK.
The QC argued there was a reasonable suspicion that the repatriation issue was being used as "a bargaining counter" and there was "the sniff of abuse about that".
Lord Justice Maurice Kay and Mr Justice Simon, sitting in London, are being asked to grant the hacker permission to seek judicial review of the Home Secretary's extradition decision.Reuse content