In order to consider whether the rise in autism diagnosis actually matters, the most important question is not whether autism is valid as a diagnostic category; rather, whether it is helpful as a diagnostic category. A scrutiny of the functions, consequences and utility of diagnosis is followed by a discussion of how diagnosis and diagnostic language has come to shape our experience. The conclusion is that diagnoses are a double-edged sword, and provoke dilemmas both for those who assign and those who receive them.