As a result of inherent cognitive and language difficulties, individuals with mental retardation/developmental disabilities often are considered difficult to assess appropriately. When cognitive and language difficulties occur in conjunction with behavioral issues, this difficulty is compounded. The IDEA requirement to include a form of assessment, known as functional behavioral assessment (FBA), is seen as one method that may reduce this problem. A description of the strengths and weaknesses of FBA, the steps in implementing the assessment, and its use with individuals with cognitive deficits as well as behavioral issues is provided. Finally, a case study simulation illustrates the process.