Cranial ultrasound examinations with 5.0 and 7.5 mHZ transducers during the first 3 days of life on 60 appropriate-for-date newborns with gestational age 24-36 wks were performed to determine the sulcal development of cerebral cortex in utero. The sulci appeared and developed in sequence. All the calcarine fissure and most of the anterior part of cingulate sulcus began to appear before 28 wks. At 28-31 wks all the whole cingulate sulcus and postrolandic sulcus, and most of the inferior temporal sulcus and covering of insula were ready to be observed. All of the insular sulci and tertiary sulci, and most of the secondary sulci from cingulate sulcus appeared after 31 wks. As cortical organization advanced, the discrepancy in the age of sulcal appearance between neuroanatomic and ultrasonic studies became less striking by the last trimester. Ultrasonic examination of the cortical sulci provides a noninvasive and convenient means to stage the normal cerebral maturation, and can be helpful in the detection of pathology in sulcal formations.