The study was designed to examine serum IL-18 level and its relation to metabolic control parameters and microvascular complications in type I diabetes mellitus (DM). Sixty two patients with type I DM and 30 healthy individuals were enrolled in the study. Serum IL-18 levels of patients with type 1 DM were significantly increased compared to controls (293.4 +/- 133.4 vs 211.2 +/- 63.9 pg/ml, P = 0.003). Patients with poor glycemic control had higher levels of IL-18 than patients with well glycemic control (329.9 +/- 141.0 vs 226.3 +/- 89.6 pg/ml, P = 0.02). There was no significant difference between the serum IL-18 levels of patients with microvascular complications and those of patients without microvascular complications (307.6 +/-:1 127.6 vs 293.2 +/- 145.6 pg/ml, P > 0.05). IL-18 correlated positively with HbA(1c) (r = 0.32, P = 0.01) and postprandial blood glucose (PPBG) (r = 0.26, P = 0.02); and negatively with HDL-cholesterol (HDL-C) (r = -0.38, P = 0.007). By linear regression analysis, PPBG was determined as the most explanatory parameter for the alterations in serum IL- 18 levels (P = 0.02). High levels of IL- 18 in patients with type I DM is related to short and long term glycemic control and HDL-C levels but not to microvascular complications. (C) 2008 Elsevier Ltd. All rights reserved.