The objective of this study was to estimate the severity of metabolic disorders at onset in children with insulin dependent diabetes mellitus (IDDM). Biochemical results taken at onset of IDDM were analysed in 158 children on their admission. Metabolic acidosis was found in 37.97% of those and ketoacidosis was confirmed in 18.99% children. Mean values of biochemical parameters are similar to those reported in the others European countries. The most severe changes of the acid-base balance parameters were observed in youngest children (1-4 y.o) living in the rural areas (pH, 7.22, HCO3- 10.2 mmol/l, BE - 16.06 mmol/l, p=0.05); this should suggest that those children are watchfully observed and IDDM should be always be considered as a possible cause of any alarming symptoms which occur.