Aims and MethodTo describe a group of prisoners who required transfer to mental health units from two London prisons. Data were collected from prison clinical records.ResultsOverall, 149 patient-prisoners were transferred over a 17-month period. Around a quarter were not previously known to services. the aggregate wait was 36.5 years (averaging between 93 and 102 days per prisoner) and the total saving to the National Health Service (NHS) has been estimated at £6.759 million.Clinical ImplicationsBoth prisons manage a large number of prisoners with untreated psychosis. While in prison, they save the NHS considerable sums of money, but transfer delays prevent timely treatment and could now be legally challenged.