The diagnostic vocabulary of a clinician appears to be specific and measurable for each clinical discipline. The diagnostic vocabulary of 11 primary care physicians over four-years' work has been analyzed. For every 1,000 patients cared for, each physician made, on average, 2,691 diagnoses every year, representing a diagnostic vocabulary of 475 different clinical entities. This vocabulary has been analyzed according to frequency of usage and clinical decision making. The clinical, teaching, and administrative implications of this analysis are discussed.