Three adult patients with a clinical diagnosis of Chiari malformation were examined by computed tomography after intrathecal injection of metrizamide via the lumbar route. In all patients Chiari malformation was demonstrated as a soft tissue oval mass at the level of C1-C2 vertebral body that was intradural and posterior to the medulla and the upper cervical spinal cord. These findings were more accurately visualized in saggital and in frontal reconstructed CTs. In one patient the spinal cord was measurably enlarged at the upper thoracic level. A delayed scan was obtained in another case at 24 hours after the injection and the syrinx was remained opacified whereas the density of cerebrospinal fluid and parenchyma decreased. In the third patient no abnormality of the cord was demonstrated either in CT or myelography. High resolution CT, especially reconstruction-CT appears to be more reliable than myelography and should be the examination of choice in the diagnosis of Chiari malformation.