The Aids Foundation says official figures on new immigrants with HIV Aids could be distorted by as much as a third.
The foundation's outgoing executive director, Rachael le Mesurier, says when a would-be immigrant is found to be HIV positive, their case is noted in statistics - even if their application to settle in New Zealand is subsequently rejected.
She says this confuses the planning for services to high-risk groups.
Ms le Mesurier says the Immigration Service, which does not keep statistics of this type, could record the number of HIV-positive people who are declined visas or residency.
She says this should be deducted from the total number of HIV diagnoses in New Zealand.