The quality of care can be perceived to have an "epidemiology" in that it is distributed in each of two populations, one of providers and another of clients. In this review of the pertinent literature, I found, overall, that the quality of technical care is better when practitioners have better or more training, are more specialized, and are more experienced though not too old; when they provide ambulatory care by appointment to a not overly large caseload in well-equipped premises and possibly in association with colleagues; and when they provide hospital care in larger institutions with significant teaching functions. I found no consistent correlation between quality and age, sex, rurality, occupation, income, and ethnicity of patients, but there were enough intimations of a relation between socioeconomic disadvantage and poorer technical care to prompt careful study.