Medical insurance organizations possess a large amount of production data from individual health care providers and from institutions. These data give insight into the type and amount of health care delivered. The number of admissions, patient days, inpatient and outpatient procedures and three specific procedures, per 100 referred patients and per 1000 insured persons, from 1986 were compared for 11 partnerships of ENT specialists located in the regions of two medical insurance organizations. The raw data were corrected for percentage of persons aged 65 years and older, the percentage of women, the referral practice of the general practitioners in the treated patient population and the number of specialists in each partnership. The differences between the partnerships with the largest and those with the smallest number of items of service amount to a factor 2.9 (admissions per 1000 insured persons) to 6.7 (septum corrections per 1000 insured persons). After introduction of the independent variables, substantial differences still exist, the lowest factor being 1.8 (hearing improvement operations per 1000 insured persons) and the highest 5.6 (outpatient procedures per 1000 insured persons). There is hardly any difference between the groups regarding a procedure with a supposedly clear indication and two procedures with a less defined indication. Further study of the causes of these differences on the individual patient level is necessary.