This is a report of a controlled, prospective, longitudinal trial of an intervention to affect medical students' attitudes toward aging. Members of the Class of 2002 at the University of Oklahoma College of Medicine were assigned a senior mentor (a community-dwelling older person) upon matriculation into medical school. Students were required to perform a structured interview with the mentor once per semester for the first 2 preclinical years and to discuss these interviews in small groups mediated by geriatrics faculty. Members of the Class of 2001 were controls. Attitudes toward aging were determined using the Aging Semantic Differential (ASD) attitude scale in August 1998 and again at the end of the second year of medical school. Initial mean ASD scores were not significantly different for the two groups. Although both classes experienced improvements in their ASD scores from Time 0 to Time 1, the improvement for the class of 2002 was significantly greater than that for the class of 2001 (2001 class mean = 0.17, 2002 class mean = 0.40, t = −3.09, degrees of freedom (df) = 219, P = .002). This difference held up under controls for sex, age, prior visits to a nursing home, prior work/volunteering in an old-age environment, and a prior course on aging (Model F = 3.00, df = 6/214, P = .008; class F = 9.70, df = 1, P = .002). It was concluded that a low-intensity intervention to introduce entering medical students to healthy older people might have a positive effect on attitudes toward aging.