In the past decade a number of studies suggested that type 1 diabetes mellitus is an oxidative stress influenced disease. Paraoxonase 1 enzyme plays a crucial role in antiatherogenic-antioxidant circle. The aim of our study was to examine the possible differences in paraoxonase 1 enzymatic activities in diabetic children associated other autoimmune diseases versus a control group. Another objective of the study was to determine if there is any difference according to the gender in paraoxonase 1 activities (arylesterase and paraoxonase activities). Paraoxonase 1 activities were determined in 51 diabetic children and 36 healthy controls. In diabetic children we determined also the C-peptide level. The paraoxonase 1 arylesterase activity was lower in diabetic females compared with diabetic males. The level of C-peptide is in an inverse correlation with the years of the disease. The paraoxonase activities have a correlation with the level of insulin antibodies in type I diabetic children. Our data suggest that paraoxonase enzymatic pattern may be different in these two activities. PON1 arylesterase activity may exhibit a tendency to low levels in women in comparison to men. The C-peptide level is a valuable tool in assessing the restant beta cell function.