Bulimia nervosa is an eating disorder of which characterized psychopathological symptoms are a recurrent episode of binge eating. The changes in cerebral blood flow (CBF) in a patient with bulimia nervosa between his or her different eating phases are presented. CBF was measured quantitatively by means of single photon emission computed tomography using I-123 N-isopropyl-p-iodoamphetamine. CBF of the global brain during a binge-eating phase was higher than that during an anorexic state phase. In the anorexic state, the CBF in the temporal, parietal, and occipital lobes on the right side was lower than that on the left side. In the binge-eating state, a lack of laterality between the right and left cerebral hemispheres was found. This finding suggests that cerebral activity differs between the two phases, and that asymmetry is dependent of the eating state.