Patently unreasonable or the patent unreasonableness test is a legal test created by common law and used in Canada by a court performing judicial review of administrative decisions. It is the highest of three standards of review, those being correctness, unreasonableness, and patent unreasonableness. Although the term "patent unreasonableness" lacks a precise definition in the common law, it is somewhere above unreasonableness, and consequently it is difficult to prove that a decision is patently unreasonable. A simple example of a patently unreasonable decision may be one that does not accord at all with the facts or law before it, or one that completely misstates a legal test.

In theory, according to the Supreme Court of Canada in Baker v. Canada (Minister of Citizenship & Immigration), this standard of review could also apply in a statutory appeal. In practice, this is highly unlikely, since the existence of a right of appeal often determines the standard of review to be correctness or unreasonableness.

Compare this to due process in U.S. law and Wednesbury unreasonableness in English law.