Statistics New Zealand says it's working hard to raise the awareness among Maori of the need to fill in a census form next month.
Community liaison adviser Luke Crawford says even though everyone is supposed to fill in a form, many Maori failed to do so in the last census in 2006.
He says more than 565,000 people who filled in forms seven years ago identified themselves as Maori, but the figure could have been more than 10,000 higher if all Maori had filled in the forms.
Mr Crawford says there's a myth that because Statistics New Zealand is a government department, any personal information it gathers can be shared with other agencies such as the police, Inland Revenue or the Ministry of Social Development.
He says that's not the case and the confidentiality of personal information is protected by law.