The debate about A2 milk has been in the public arena for at least five years. There have been lots of claims and counter claims about whether ‘ordinary milk’, which is a mixture of A1 and A2 milk, is linked to a range of disease conditions, and whether selecting for cows that produce only A2 milk can avoid these problems. Despite the claims and counter claims, the substance of the arguments has not been widely aired in public. Instead, most people have only heard the assertions. Therefore it has been a case of making a judgement as to which of the two competing sides has most credibility. In early August 2004 the New Zealand Food Safety Authority (NZFSA) released the ‘Swinburn Report’ (Swinburn 2004). The NZFSA had contracted Professor Boyd Swinburn back in March 2003 to review the scientific evidence for and against the A1/A2 hypothesis. Depending on which media report people were exposed to, it would have been reasonable to accept either that the Swinburn Review had found that there was no difference between A1 and A2 milk, or that there were indeed significant concerns about the health implications of A1 milk. And so the issues remain as muddy as ever. The purpose of this paper is to present the evidence for and against. In that way dairy farmers and their consultants can make their own judgements as to whether or not this is an issue that they need to be concerned about.