This paper explores mistake of fact as a ground of judicial review in New Zealand. In part II I introduce a range of basic points, including the evident attraction of mistake of fact as a ground, and the state of authority on it. The New Zealand position remains unsettled, contrary to suggestions in leading texts. In England, by contrast, the ground is established at Court of Appeal level by E v. Secretary of State for the Home Department [2004] EWCA Civ 49, [2004] QB 1044.In part III I argue that New Zealand courts might be justified in following the English Court of Appeal in E and adopting mistake of fact as a ground of review, so long as they also adopt at least one of the limiting criteria set out in E: that the fact in question must be established in the sense that it could have been shown by objective and uncontentious evidence. I argue that this criterion should be understood as comprising two aspects which respectively serve to avoid application of each of the two rationales for limiting review of factual determinations.First, where the fact in question is established in the sense of not requiring resolution of conflicting evidence, this neutralizes the objection that judicial review is not an appropriate procedure for resolving disputed issues of fact. And secondly, where the fact in question is established in the sense of not requiring evaluative judgment, this meets the objection that judgment and evaluation are the proper domain of the decision-maker, and that a reviewing court should intervene into that domain only where a decision is unreasonable. This second requirement is met in relation to findings of primary facts, and excludes from the scope of mistake of fact review any findings that involve evaluation of accepted primary facts for the purposes of applying a statutory test. The latter type of case is appropriately dealt with by other grounds.