The development of nine infants with enlarged subarachnoid spaces identified by specific CT-scan criteria was prospectively followed to two to three years of age. Infants with intracranial hemorrhage, CNS anomaly, microcephaly or other factors of potentially major negative impact on their development were excluded. All study infants had normal or only minimally increased ventricular size and none developed hydrocephalus. Head circumference was greater than or equal to 90th percentile in all cases, and six fathers also had a head circumference greater than or equal to 90th percentile. Six infants had gross motor delay and mild hypotonia in the first year. One, born at 30 weeks gestational age, had transient dystonia. At follow-up all the infants were developing normally, apart from four with minor concerns. Infants with macrocephaly or rapid head-growth, CT-scan findings of enlarged subarachnoid spaces and normal to minimally increased ventricular size, and who have a parent with macrocephaly, have a good developmental prognosis and a characteristic pattern of neuromotor development in the first year.