Case studies are an accepted method for reporting treatment outcomes. However, to be useful and authentic, a systematic and principled approach to collecting, analyzing, and reporting case data must be observed. This paper proposes a basic case study format for documenting augmentative and alternative communication (AAC) intervention to ensure reliable and valid measurement of performance and outcomes for evidence-based practice. An example case study of an adult with cerebral palsy who relies on AAC is presented to show how the principles of evidence-based practice (EBP) and performance measurement were applied to the AAC assessment process. AAC service delivery requires performance and outcomes measurement to lead to effective communication and improved quality of life. Reliable and validated methods of reporting data allow for consistency and the comparison of performance and outcome measures so decisions are not based on impressions of effectiveness, but actual results. (Contains 3 tables and 1 figure.)