Relevance. The relevance of the study is due to insufficient data on the early development of preterm infants without a history of local brain lesions and any somatic or neurological pathology. Intention. To analyze development of neurocognitive functions of preterm infants during periods of maximum synapse formation in the primary sensory and prefrontal cortex of the brain, as well as during periods of decrease in this process in the above-mentioned areas of the cortex. Methodology. A longitudinal study of neurocognitive development in preterm and full-term children aged 5 to 24 months was conducted. The study involved 24 preterm children and 51 full-term children, who were examined at 5, 10, 14 and 24 months (with age adjustment for preterm children). Bayley Scales of Infant and Toddler Development (3rd edition) were used to assess 5 domains: cognitive development, receptive and expressive communication, fine and gross motor skills. Results and Discussion. The preterm children demonstrated decreased neurocognitive functioning compared to their full-term peers during periods of decline in active synaptogenesis, while during periods of maximum synapse formation, preterm children demonstrated normal development. Conclusion. The data obtained can be used to create early development programs for preterm children.