National survey data were used to describe and analyze the treatment of selected illnesses: hypertension, heart condition, hernia, gynecological infection, menstrual disorder, other gynecological conditions, pneumonia, and urinary tract infection. The number of office visits, the rate of diagnostic testing, the average charge, and the use of inpatient and outpatient hospital services were analyzed in an econometric model of treatment. Differences in the treatment of patients with similar illnesses were associated with comprehensive insurance, the availability of hospital and physician resources, and other economic considerations. There was also evidence that hospital and ambulatory services were substituted for each other, as a result of economic as well as medical considerations.