Congenital hyperinsulinism (CHI) is the most common cause of severe persistent hypoglycemia in neonates and infants. Early diagnosis and effective treatment (based on the principles of pharmacogenetics) play the key role for the prognosis. The DNA anlysis, which can identify mutation in one of the 11 genes causing MODY, is crutial in the diagnostics. Moreover, The genotype determines also the optimal therapy approach (medicaments, diet or rarely surgery). There was a large progress of novel medicaments treating particularly most severe (diazoxide-resistant) forms of CHI.Key words: congenital hyperinsulinism - diazoxid - DNA analysis - hypoglycemia - somatostatine analogues.