Development of improved outcome measures for Alzheimer's disease (AD) clinical trials is a major objective of the Alzheimer's Disease Cooperative Study (ADCS), an NIA-sponsored, multisite clinical trials consortium. The ADCS is committed to recruiting and following minority patients in clinical trials. At present, a serious impediment to recruiting non-English-speaking minorities is the lack of instruments with adequate translation. Because Spanish is the second most commonly spoken language in the United States and because persons of Hispanic origin represent approximately 10% of the population, we conducted an instrument development protocol for Spanish-speaking patients. Evaluating treatment efficacy in Spanish-speaking AD patients requires the development of assessments that are comparable to those used for English-speaking participants in clinical trials. The ADCS Instrument Development Project evaluated the sensitivity, reliability, and validity of new or improved measures in each of five assessment domains: (a) cognition (immediate and delayed memory, praxis, attention, and executive function); (b) clinical global change; (c) activities of daily living; (d) behavioral symptoms (agitation and other noncognitive symptoms); and (e) cognition in severely impaired patients. These new treatment efficacy instruments were translated for Spanish speakers and a Spanish Instrument Study was conducted in parallel with the English version of the study. This report describes instrument translation, entry criteria, and recruitment procedures. In addition, the demographic and clinical characteristics of the cohort at baseline are presented and compared to the English-speaking cohort. Implications for the development of comparably sensitive Spanish language instruments are discussed.