This article describes the development of the protocol for the Clinical Antipsychotic Trials of Intervention Effectiveness (CATIE) Alzheimer's disease trial, which was developed in collaboration with the National Institute of Mental Health to assess the effectiveness of atypical antipsychotics for psychosis and/or agitation occurring in outpatients with Alzheimer's disease. The article provides a detailed description of the methodology used in the trial as well as the clinical outcomes and effectiveness measures incorporated into it, discussing the most salient issues encountered in developing the design of the trial, as well as the unique features of the trial.