Fonterra chairman John Wilson has stood down from the role after a serious health scare.

The dairy cooperative announced this morning that Wilson will remain a director on its board until its annual meeting in November, when he will retire from the board.

The company said in a statement that Wilson had undergone a significant surgery within the last month and would require ongoing treatment.

Existing director John Monaghan will be the new chairman. He has been on the board of Fonterra since 2008.

Wilson said the decision to stand down as chair had been difficult but was ultimately in the best interests of the cooperative.

"I have made a very good recovery and am well but will need on-going treatment.

"It has been a privilege to serve you as chairman and give something back to this great co-operative that continues to give my family and me so much.

"As many of you will know from experience, governance roles are incredibly rewarding, but equally demanding on the individual and their families.

"Continuing as chairman when I cannot put my full energy and attention into the role is not appropriate."