We present an overview of the role of the trial coordinator in the Diabetes Control and Complications Trial (DCCT). The DCCT is a multicenter clinical trial designed to examine the effects of two different diabetes treatment regimens on the appearance and progression of the early vascular complications of IDDM. Although the specific responsibilities assumed by the trial coordinators differ from center to center, in general they include administration, recruitment, eligibility testing, and patient management. The trial coordinator's role has evolved with the needs of the DCCT, and may serve as a model for other large multicenter trials.