We conducted an analysis of all complaints received in a busy suburban emergency department during 1985. All complaints were handled in a standardized fashion, and were categorized as billing, physician, nursing, or miscellaneous. Data were expressed as a "complaint frequency" (complaints per 1,000 patient visits). Complaints were analyzed for the following characteristics: reason, gender of the patient, gender of the complaining party, relationship of the complaining party to the patient, health care provider, patient age, and patient disposition. The chi-square method was used to identify characteristics associated with a high risk for complaints. There were a total of 244 complaints, arising from 64,910 patient visits, yielding an overall complaint frequency of 3.8. The largest number of complaints (135), involved billing (frequency, 2.0). The most common (60) was insurance carrier rejection of the bill as a nonemergency. The next most common billing complaint (25) was a charge mistakenly billed too high by the ED. There were 70 complaints regarding emergency physicians, for a complaint frequency of 1.1. Of these, 17 were due to a perceived lack of communication with the patient, the patient's family, or the patient's private physician. Eighteen complaints were regarding a perceived misdiagnosis. One physician had a significantly higher complaint frequency than the group as a whole (P less than .005). There were 17 complaints regarding the nursing staff, for a complaint frequency of 0.2. Twenty-two complaints were classified as miscellaneous. Expressing data as complaint frequencies allows comparison of trends in a department, staff members, and different EDs with varied patient populations.(ABSTRACT TRUNCATED AT 250 WORDS)