Policymakers, managed care organizations, medical educators, and the general public are showing an increasing interest in the amount and quality of care provided by generalists and subspecialists. This article reviews studies comparing the knowledge base of and quality of care provided by these 2 groups of physicians. English-language articles were identified through MEDLINE (1966-present) using the following keywords: generalist, generalism, (sub)specialist, (sub)specialty, (sub)specialization, consultation, referral, and quality of care, and through the bibliographies of these citations. All studies were evaluated. With respect to quality of care, only American studies were chosen. Data quality was assessed by me. Evidence is strongest that the knowledge base and quality of care provided by specialists exceeds those of generalists for certain conditions such as myocardial infarction, depression, and acquired immunodeficiency syndrome. Differences in many other areas are multifactorial, and often a function of study design or patient selection. The differences, however, are not as striking or important to the health of the public at large as those deficiencies in disease management, preventive care, and health maintenance that are common to all physicians. Furthermore, overuse of diagnostic and therapeutic modalities by certain specialists leads to increased costs with either no benefit or added risks to patients. The quality and coordination of care provided by generalists and specialists may be improved through changes in education and training, via quality improvement methods of providing patient care, and by increasing visit length and optimizing use of referrals and strategies for generalist-specialist comanagement. Further study of these areas is warranted and should concentrate on outcomes.