PURPOSE: To ascertain the sonographic changes of cerebral development in the newborn infant according to the postconceptional age and to assess the sonographic predictability of postconceptional age. MATERIALS AND METHODS: Retrospectively, 251 consecutive normal brain sonograms were analyzed. The postconceptional age of the newborn infant ranged from 26 to 44 weeks(male : 123, female : 128). We made a score with sonographic patterns of the sylvian fissure, the sulcal development, the echogenecity of periventricular white matter(PVWM), and the cortex-subcortex(C-SC) differentiation. The scoring systems were as followed; Open Y-shape(a point) and close Y-shape(two points) of the sylvian fissure : Lissencephalic pattern(a points), intermediate pattern(two points), and mature form (three points) of the sulcus : Discrete increased echogenecity of PVWM along the entire lateral ventriclular wall (a point), indistinct margin and intermediate extent (two points), and faintly localized to trigonal area(three points) of PVWM echogenicity : Indistinct (a point), broad and faint (two points), and defintiely linear (three points) C-SC differentiation. We identified the sonographic developmental change according to postconceptional age. And we classified the maturity of brain with 15 grades using the sonographic score. Correlation between the sonographic grades for cerebral development and the postconceptional age were statistically analysed. RESULTS: Sonography showed immature brain(score 1 for sylvian fissure, sulcal pattern, echogenecity of PVWM, and C-SC differentiation) until 28 postconceptional weeks(PCW) of the newborn infant. All sylvian fissures had been converted to close Y-shape until 35 PCW. Mature form for sulcal pattern, echogenecity of PVWM, and C-SC differentiation appears since 34-35 PCW. Conversion to the mature forms was detected in about 98% (191 out of 194 cases) of sulcal pattern after 38 PCW, all cases of echogenecity of PVWM after 40 PCW, and C-SC differentiation after 41 postconceptional weeks. And sonographic grades for cerebral development were well correlated with the postconceptional age(r = 0.90, p < 0.0001). CONCLUSION: Morphologic changes of the sylvian fissure, the sulcal pattern, the echogenecity of PVWM, and the C-SC differentiation on sonography were identified with increasing postconceptional age. And sonographic grades were well correlated with the postconceptional age. In conclusion, sonography may be a convenient and helpful method to evaluate the cerebral developmental changes of the newborn and to predict the postconceptional age.