A 10% household sample of high- and low-income census tracts was interviewed to assess the extent of doctor shopping. In 632 households studied, 53% of high socioeconomic status and 51% of low socioeconomic status families had shopped for or changed doctors of their own volition. During the previous year, 4% of each socioeconomic group had consulted more than one doctor without referral for the same episode of illness. Shoppers could be distinguished from non-shoppers--shoppers were younger, were better informed about medical specialties, were less self-reliant, more hypochondriacal, expressed less hostility towarn physicians, and had less positive attitudes toward the medical care system. The differences between shoppers and non-shoppers were generally similar for both high and low socioeconomic status groups. In addition, 52% of the families studied had been forced to change doctors because of circumstances beyond their control, i.e., the patient moved or the doctor moved, retired, or died.