A man has been jailed for four years after admitting he raped an eight-year-old girl with spina bifida over a two-year period.

Riwhi Strongman, 68, from Auckland, appeared in the High Court at Rotorua yesterday for sentencing after pleading guilty to a representative charge of rape.

Mr Strongman's jail term was reduced by two-and-a-half years because he had already served prison time for attempted rape and indecent assault on the girl's sister during the same period.

Justice Lester Chisholm said the sentencing was "not easy" as he had to take into account what was known in legal terms as "totality".

Setting the starting point for Mr Strongman's prison term at five years, Justice Chisholm added three years for aggravating features, such as the vulnerability of the sick girl and his previous convictions but deducted 18 months for Mr Strongman's guilty plea.

Justice Chisholm said he had no choice but to reduce the sentence further because Mr Strongman was jailed in 1993 for three-and-a-half years for offences relating to the same period.

He was also jailed in 1984 for nine months for indecently assaulting another girl aged under nine years.

Not reducing the sentence to take that into account would mean Mr Strongman would have been jailed for more than 10 years for the entire offending, Justice Chisholm said.

"That would be much too high so I need to make some kind of adjustment for the totality principle."

Crown prosecutor Prue McGuire argued Mr Strongman should not be given the benefit of totality because he had the chance to admit his offending when he was sentenced in 1993. The court heard Mr Strongman raped the girl between 1981 and 1983.

Although Mr Strongman pleaded guilty to the representative charge of rape, which means the rape happened on more than one occasion, he argued it only happened once.

However, the rapes happened on about 15 occasions.

Justice Chisholm said the victim, who was at court yesterday, had suffered both physically and emotionally. "I find the victim impact statement distressing reading.

"It is appropriate that he is being sentenced in her presence today and it might allow her to go on with a life that she has not been able to get on with."

Chris Tennet, who represented Mr Strongman, said credit should be given to his client because he had not offended in 20 years, which was probably associated with him dealing with his alcohol problem.