Clinicians rigorously study diseases and disorders so that they can formulate the best set of criteria for diagnosis. However, it is often the case, particularly on a college campus, that a friend would notice changes in physical or mental wellness long before a doctor or psychologist would. Because of this, research on the accuracy of lay diagnosis is needed. The purpose of the present study was to introduce a new measure designed to determine how accurate college women are in their judgments about the point at which a target woman has an eating disorder, based on symptoms of being underweight, exercising excessively, limiting caloric intake, and self-induced vomiting. The present research is important because problematic behavior that is diagnosed too late might result in women delaying treatment until symptoms have progressed. With eating disorders, as with many psychological disorders, early intervention provides the best conditions for recovery, so encouraging early detection and referral is crucial.