The authors developed an exercise to teach medical students counseling skills for promoting change in health-related behaviors using trained patient instructors (PIs) who enact the patient role, perform a standardized evaluation of the interview, and provide instructional feedback. Third-year medical students in two consecutive academic years at the University of Rochester School of Medicine and Dentistry received either feedback from a faculty member on a videotaped interview between the students and a simulated patient (SP) or direct feedback from a PI immediately following the students' interview with the PI. The students in the PI group gave higher ratings to the realism and effectiveness of the interview session than did students in the SP group. Students in both groups rated PI feedback as more helpful than videotaped review, even though they had experienced only one of these two methods. This exercise represents a new use of patient instructors that may also be applicable to teaching counseling skills in other areas of behavioral medicine.