The primary goal of medical education is to foster development of clinical competence in trainees at all levels. Variable clinical experience, inconsistent methods of instruction, and ambiguous evaluation criteria undermine this goal. Standardized patients, trained to consistently portray a wide variety of clinical cases, can help overcome many of these educational problems. This article describes the development and application of standardized patients throughout medical training at The University of Texas Medical Branch, Galveston, in the freshman interviewing course, the second-year physical diagnosis course, third-year clerkships, a fourth-year final exercise, and residency training. Development of this program is discussed in the context of a broader literature in medical education, and investigation of variables affecting standardized patient and student performance is reported. Future directions for use of standardized patients in monitoring and promoting the development of clinical competence are discussed.