A third of people sentenced to life in prison are in the community on parole.
Hardliners on crime say this makes a mockery of the term life imprisonment, but the Ministry of Justice says it is an accurate description as people on parole can be recalled to jail.
Figures issued by the Department of Corrections under the Official Information Act show that of the 719 people serving life sentences, 217 have been freed on parole.
The figures go back to 2002. There may be more prisoners on parole who were freed earlier, but this information could not be reliably extracted from electronic records.
Sensible Sentencing Trust spokeswoman Ruth Money said the public would be "shocked to learn the true definition" of life imprisonment. "The terminology is counter-intuitive at best, although most victims and survivors we assist believe it is deliberately misleading," Ms Money said.
"It is devastating for victims to hear 12 years or life imprisonment handed down by a judge in sentencing, for example, only to then learn the real meaning and true likelihood of time served."
A ministry spokesman said it had considered the term "life imprisonment" during policy work on the Sentencing Act 2002 but concluded it was accurate.
He said any offender sentenced to life imprisonment could be recalled to jail for various reasons for the rest of their life.
The "three strikes" legislation of 2010 meant some offenders could be sentenced to prison without the possibility of parole.
The figures also show 34 of the 314 people serving preventive detention are on parole.
A life sentence is usually imposed for murder and can be imposed for manslaughter and class A drug offences.
Preventive detention is usually imposed for serious violent or sexual offenders who pose a significant and continuing risk.
Offenders serving life sentences become eligible for parole after serving 10 years, unless they have been sentenced to a longer non-parole period.
Those given preventive detention become eligible for parole after five years in prison (10 years if sentenced before 2002) unless they have been sentenced to a longer non-parole period.
Anyone on parole for either of these sentences is subject to conditions for the rest of their lives and can be recalled to prison.
Corrections deputy national commissioner Maria McDonald said the independent Parole Board made public safety the "paramount consideration" before granting parole.
Rethinking Crime and Punishment spokesman Kim Workman said prisoners serving life were spending more time in prison than they did historically and there was no cause for alarm.
Serving life: 502 in prison - 474 men, 28 women - including 73 in Rimutaka Prison, 71 in Spring Hill Corrections Facility, 63 in Christchurch Men's Prison, 54 in Auckland Prison, 21 in Hawke's Bay Prison, 45 in Whanganui Prison and 16 in Manawatu Prison.
6 aged 15-19, 82 aged 20-29, 5 aged 65 and over.
11 for sexual offending, three for drugs and anti-social behaviour, 488 for violence.*
217 on parole - 200 men and 17 women.
All convicted of violent offending.
An average of 20 paroled each year since 2002-03. Most was 27 in 2002-03. Least was 9 in 2007-08
Serving preventive detention: 280 in prison: 279 men, 1 woman, including 49 in Rimutaka Prison, 48 in Auckland Prison, 33 in Whanganui Prison, 29 in Christchurch Men's Prison, 26 in Spring Hill Corrections Facility, 18 in Hawke's Bay Prison, 4 in Manawatu Prison.
The youngest is a man aged 25-29. The oldest three are 75-79.
31 for violence, 248 for sexual offending and one for dishonesty.*
34 on parole - all men, seven are aged under 40, four aged 65 and over.
29 convicted of sexual offending, five for violent offending.
17 released in the last three years and 17 released in the preceding seven years.
* This is the most serious type of offending for which inmates were sentenced. They may also have committed other offending.
Note: Seventeen of those offenders in prison on a life sentence have also been sentenced to preventive detention. Three others sentenced to both have been freed on parole.
- The Dominion Post