Conclusions: It is presumed that brain is susceptible to oxidative damage provoked by 3-MCG and that this pathomechanism may contribute to the neurological dysfunction characteristic of the patients affected by 3-MCCD. The girl now 4.5-year-old, at age of 3 yrs was admitted to our Dept, because glycaemia 500 mg/dl. Diabetes mellitus type 1 was diagnosed.