The aim of the research was to determine the diagnostic significance of Brain-derived neurotrophic factor (BDNF) in preterm infants with gestational age less than 34 weeks. The study group included 30 preterm infants with average birth weight 1373.5±66.0 g and gestational age 29.3±0.5 weeks. The catamnestic observation was conducted over this category of infants until reaching the corrected age of 18 months. The relationship between BDNF levels and antenatal factors, postnatal results and remote effects were determined. Premature infants who were diagnosed with disability at the corrected age of 18 months, had the lowest BDNF concentrations at 5-7 days of life (142.1±64.7 pg/ml, р<0.05). BDNF concentrations were still low at the 4th weeks of life - 166.7±69.5 pg/ml, р<0.01. The above data correlates with fertility problems of the mothers (r=-0.74, р<0.05). BDNF concentrations at the 5-7 days of life also correlated with the development of retinopathy of prematurity (r=0.58, р<0.05). Insufficient activity of neurotrophic factors (BDNF) that enable the functional activity of neurons during hypoxia, causes low MDI and CDI (less than 69) at the corrected age of 18 months (r=0.63, r=0.78 respectively, р<0.01). The paper shows the changes in BDNF concentrations during the neonatal period of preterm newborns with gestational age less than 34 weeks.