North Shore MP Wayne Mapp has announced his intention to stand down at the next election.

In a media statement issued this afternoon, Dr Mapp, 58, said he was leaving "for personal and family reasons" after 15 years in Parliament.

He was appointed Minister of Defence and Minister of Research, Science and Technology after National won the 2008 election.

"I have been privileged to serve as the Member for North Shore since 1996, and more recently, to serve in the Cabinet under Prime Minister John Key," he said.

"When the election is held I will also have completed three years in Cabinet. In both the Defence, and Science and Innovation portfolios, I have set a strategic direction that is intended to be enduring."

Dr Mapp said over the next year he would be working on implementing the Defence White Paper and "strengthening and diversifying New Zealand's science system".

"In 2011 I will be focusing on supporting research commercialisation, building our core science infrastructure and promoting further business growth through successful innovation, Dr Mapp said.

He said he looked forward to supporting National's next North Shore candidate for the 2011 election. North Shore has been a safe National seat for decades.

He later told reporters he was not unwell, nor were any members of his family.

He would not discuss the "personal and family reasons" referred to in his retirement announcement.

Prime Minister John Key congratulated Dr Mapp on a 15-year political career, being appointed to Cabinet and being a "very effective" MP for North Shore.

"We're obviously very sorry to lose him but we recognise that he is putting his family first," Mr Key told reporters.

Mr Key said he had "some idea" about the family reasons Dr Mapp had referred to but was not going to talk about them.

Dr Mapp has a PhD in international law from Cambridge University and lectured in commercial law at the University of Auckland before entering politics.