Evidence-based practice (EBP), a framework that originated in clinical medicine, offers a principled means of addressing longstanding questions about clinical practice in communication disorders. However, in several respects EBP represents a radical departure from traditional thinking in speech-language pathology and audiology. In this paper, I first describe some of the ways in which the EBP orientation challenges conventional wisdom. I then describe criteria from the EBP literature to be used in evaluating evidence on diagnostic procedures. Using EBP criteria to design, conduct, and interpret studies will increase the quality of evidence available to support clinical decision-making in communication disorders, and to the credibility of the field as a whole. Learning outcomes: (1) Readers will be able to explain why rigorous scientific studies provide a stronger basis for clinical decision-making than do the opinions of authorities. (2) Readers will be able to list five EBP criteria for evaluating a study of diagnosis. (3) Readers will be able to describe and interpret two measures of diagnostic accuracy. (4) Readers will be able to explain the limitations of small-sample studies of diagnostic procedures.