OBJECTIVE: To compare direct medical costs of the treatment of type-2 diabetic patients with hypertension, hyperlipidemia, and no comorbidity. METHODS: The study used an integrated medical and pharmacy claims database from the Hawaii Medical Service Association. Patients with at least one paid medical claim in the calendar year 1995 for type-2 diabetes mellitus were selected. Subsequently, these patients were segregated into three mutually exclusive categories: patients with hypertension as the sole comorbidity (Nhtn), patients with hyperlipidemia only (Nhlpd), and patients with no recorded comorbidity (Nnoco) in 1995. Average and median total medical treatment costs as well as medical costs for the treatment of diabetes and commonly associated comorbidities were estimated for each population. RESULTS: Table 1 shows sample size, age and gender distributions of three populations. Table 2 shows the total medical and diabetes and associated comorbidity related medical costs of treatment. Table 1. Demography Populations Sample size Age % female Average Median Nhtn 808 52 53 51.1 Nhlpd 657 50 51 47.6 Nnoco 623 45 47 52.3 Table 2. Medical costs ($) Populations Total Diabetes and associated comorbidities Average Median Average Median Nhtn 1,964 471 427 184 Nhlpd 1,197 571 374 225 Nnoco 2,735 456 594 166CONCLUSION: Average medical costs of treatment were the highest for patients with no recorded comorbidity in 1995. In contrast, the median cost estimates were the lowest for these patients. Results indicated that distributions of medical costs were positively skewed; the observation was most prominent in the population with no recorded comorbidities associated with type-2 diabetes mellitus. This finding may result from several factors including coding, severity, and/or compliance.