Southern Cross says increasing the premiums for its older policy holders has been unavoidable.
The cost of premiums for a retired couple has risen by about 25% in the past two years.
Southern Cross is New Zealand's largest heath insurer, with about 830,000 members - including about 100,000 aged over 65.
Chief executive Peter Tynan told Nine to Noon that group accounts for about one third of all claims and their premiums are based on their experience from the previous year.
He says no margins are built into the premiums, as Southern Cross is not for profit.
But Mr Tynan says the society will be reviewing the premiums for older members.