The most common diagnoses of elderly patients in the emergency department (ED) were compared among three age subgroups: 65 to 74, 75 to 84, and 85 and older. The computerized billing records for patient visits to 10 northern New Jersey hospital EDs for the years 1985 to 1991 were retrospectively analyzed. The most frequently occurring ICD-9-CM codes for elderly patients were compared among the three age subgroups. Elderly persons comprised 174, 146 (14% of the total) patient visits. The 176,146 patient visits were assigned 259,440 ICD-9-CM codes. The most common ICD-9-CM codes for medical diagnoses included chest pain, cardiac dysrhythmias, congestive heart failure, syncope, abdominal pain, and dyspnea. Fractures, particularly of the lower limb and upper limb; contusions; open wounds, particularly of the head, neck, and trunk; and falls were among the most common trauma diagnoses. The proportions in the three age subgroups of each diagnosis were statistically significantly different, except for cardiac arrest and contusions of the trunk and of multiple sites. The diagnoses with clinically significant higher relative risks in older age subgroups were atrial fibrillation, congestive heart failure, syncope, hypovolemia/dehydration, gastrointestinal hemorrhage, dyspnea, pneumonia, pulmonary edema, cerebrovascular accident, septicemia, urinary tract infection, fractures, and open wounds of the head, neck, trunk, particularly the scalp, and falls. Clinically significant lower relative risks were found in older age subgroups for chest pain, acute myocardial infarction, hypertension, angina, chronic airway obstruction not elsewhere classified, epistaxis, contusions of the upper limb, and open wounds of the finger.