Medical schools' affirmative action policies traditionally focus on race and give relatively little consideration to applicants' socioeconomic status or "social class." However, recent challenges to affirmative action have raised the prospect of using social class, instead of race, as the basis for preferential admissions decisions in an effort to maintain or increase student diversity. This article reviews the evidence for class-based affirmative action in medicine and concludes that it might be an effective supplement to, rather than a replacement for, race-based affirmative action. The authors consider the research literature on (1) medical students' socioeconomic background, (2) the impact of social class on medical treatment and physician-patient communication, and (3) correlations between physicians' socioeconomic origins and their service patterns to the disadvantaged. They also reference sociological literature on distinctions between race and class and Americans' discomfort with "social class."