In response to two written clinical vignettes describing patients with commonly seen somatic and psychologic complaints, 146 physicians from internal medicine, family medicine, and psychiatry recorded the tests and initial treatments they would order. As with the problems and diagnoses suggested by the physicians, enormous variation was seen in all specialties. The number and to some extent the nature of tests, procedures, and initial treatments ordered varied by specialty and within specialty subgroups (i.e., housestaff, full-time academic, and volunteer clinical faculty members). Physician test ordering responses to one vignette was highly correlated with responses to the second vignette, suggesting that test ordering among physicians is partly based on personal habits and characteristics and not alone on the patient's signs and symptoms.