The authors report 18 infants with benign enlargement of the subarachnoid spaces seen at their institution during a 1-year time interval. This condition is characterized by the computerized tomography findings of dilatation of the subarachnoid spaces, normal or slightly enlarged ventricular size, and prominence of the basilar cisterns. Most cases were found in children referred for the evaluation of abnormally increasing head circumference measurements. Although it was not possible to document the development, and, in several cases, improvement of this process, in these patients enlargement of the subarachnoid spaces was a benign diagnosis, not associated with serious neurological dysfunction.