The aims of this study were (1) to compare N-isopropyl-p-[I-123]-iodoamphetamine (123I-IMP) SPET with computed tomography (CT) in chronic-stage head trauma patients with neurological abnormalities and (2) to quantify regional cerebral blood flow (rCBF) in patients with chronic-stage head trauma. 123I-IMP SPET and CT were performed in 23 patients with chronic-stage head trauma and 12 normal controls. Both types of imaging were evaluated visually. In addition for the SPET images, the rCBF in 12 regions (bilateral frontal cortex, temporal cortex, parietal cortex, occipital cortex, perilolandic area, cerebellum: total 276 regions) was analysed quantitatively using a reference sampling method. In total, 39 focal lesions related to neurological abnormalities were detected. Although 22 (56.4%) lesions were observed using both CT and SPET, another 17 (43.6%) were detected by SPET only. The mean rCBF in the localized lesions of each lobe, which correspond to low-density areas (LDAs), were lower on CT than those of each lobe seen only on SPET. These rCBF values were lower than the mean rCBF values in the lobes of the controls. The mean rCBF values in each lobe with visually normal tracer uptakes were also significantly lower in the 23 patients than in the controls. 123I-IMP SPET is useful for demonstrating brain dysfunction in morphologically intact brain regions and for providing objective evidence to account for the clinical presentation of patients presenting with chronic traumatic brain injury.