We describe an adult with Rasmussen's encephalitis associated with widespread decreased accumulation of tracer on 123-I iomazenil (IMZ) SPECT. The patient had a form of epilepsia partialis continua and neurological deterioration associated with hemiatrophy. Cranial MRI showed cerebral atrophy in the left frontal, parietal, and temporal lobes, without abnormal intensity. Delayed IMZ SPECT showed widespread decreased accumulation of tracer in the left temporal and frontal regions. An early scan showed mildly decreased accumulation in the left temporal and frontal regions. Three-dimensional stereotactic surface projection (3D-SSP) analysis showed that the decreased regions on delayed IMZ images were slightly larger as compared with the previous IMZ study performed. Some regions without decreased accumulation of tracer on Tc-ECD or early IMZ images showed decreased accumulation on delayed IMZ images. This case study suggests that benzodiazepine receptors may be reduced in the affected hemisphere of patients with Rasmussen's encephalitis.