In a review of CT scans of 6,078 patients, 47 patients with well documented leptomeningeal infections were identified; 45 were infants or children. Most of the infections were bacterial; 53% were due to Haemophilus influenzae. The 47 patients were divided into two groups according to whether the initial scan was obtained during the acute illness (group A) or after initial treatment had been completed (group B). The 30 patients in the acute group A had 24 complications: 18 with areas of diminished attenuation in the brain parenchyma and six with dilated ventricles. Eleven patients had initially normal scans, but three of these subsequently developed complications. In group B, the 17 patients had 28 complications: nine with enlarged ventricles; eight with subdural effusion; seven with areas of diminished attenuation; and four with abscess formation. An unusually high percentage (40%) of the patients with areas of diminished attenuation had involvement of the anterior poles of the frontal lobes. Of the patients who showed this predilection for the frontal lobes, 72% had Haemophilus influenzae meningitis. CT was found to be useful in early detection of complications of leptomeningeal infections, as well as in evaluation of the extent of the lesions.