We examined whether four patient characteristics (age, ethnicity, sex and appearance) influenced five physician behaviors with the patient (interviewing, nonverbal attention, courtesy, information giving and empathy). Ten physician-patient interactions were observed through a one-way mirror for each of 15 physicians. Physicians were rated higher on information giving (p = 0.002) and empathic skills (p = 0.02) when they were with female patients; on interviewing (p = 0.02) and empathy (p = 0.0007) with Anglo-American compared with Spanish-American patients; on interviewing (p = 0.01), nonverbal attention (p = 0.001) and courtesy (p = 0.02) when with the best groomed patients; and on courtesy (p = 0.03) with elderly patients. In addition, there were fewer physician-initiated interruptions with female patients (p = 0.03) and with well-groomed patients (p = 0.02). Each of the four patient characteristics studied acted independently in influencing physician behavior. The recognition that patient characteristics influence physician behavior should stimulate physicians to examine their reactions in order to insure that all types of patients receive thorough, courteous and empathic care.