Traditional methods of diagnosis are of little therapeutic use when diagnostic criteria are based upon topographical rather than functional aspects of behavior. Also, this sentence in the original seemed rather awkward and a bit unclear. In contrast to this, several authors have put forward experience avoidance disorders as an alternative which takes functional criteria into account. This case study presents the analysis and treatment of an anxiety disorder following the formulation of functional analytic psychotherapy. This psychotherapy is based on a therapeutic relationship which puts particular emphasis on natural reinforcement and eventualities which occur in a clinical context, relating them to a natural context, and establishing functional equivalences. The different stages of the treatment are described and details are given of the therapeutic relationship and the monitoring of the results over a period of 18 months.