Background: The aim of this study is to determine the relationship between oxidative stress marker (8-iso-prostaglandine F 2α ) and glycemic indices computed from daily glucose monitoring data in children with type 1 diabetes mellitus (T1DM). Methods: Thirty-one children and adolescents with T1DM (median age 12.2 years) and healthy subjects (median age 11.7 years) were enrolled into the study. Anthropometric data were recorded for the entire group before the study. In addition, diabetes duration, insulin requirement, lipid values, microalbuminuria, HbA 1c were recorded in T1DM subjects. T1DM subjects performed self-monitoring of blood glucose (SMBG) for a month (at least four times a day) for calculating glycemic indices. Twenty-four-hour urine 8-iso-prostoglandine F 2α levels were studied at the end of the study period in the both groups. Results: Median diabetes duration was 5 years, hemoglobin A 1c (HbA 1c ) was 7.3%. Standard deviation (SD) of the blood glucose (BG) was determined as 85 mg/dL. Median urinary 8-iso-prostoglandine F 2α was found to be significantly higher than that of the healthy subjects (2808.9 and 298 pg/mg creatinine, p<0.001, respectively). There was no correlation between urinary 8-iso-prostoglandine F 2α and age, anthropometric data, diabetes duration, insulin requirement, lipid values, microalbuminuria, HbA 1c , or SD of BG in T1DM groups. Conclusions: This study showed that, 8-iso-prostoglandine F 2α that is an oxidative stress marker, is significantly higher in T1DM than that of healthy subjects while, no significant relation between glycemic indices and urinary 8-iso-prostoglandine F 2α levels were demonstrated. Further studies are needed to assess other factors, and the relationship between glucose fluctuations and oxidative stress markers.