Frontotemporal dementia (FTD) often coexists with motor neuron disease (MND). To characterize glucose hypometabolism in patients with FTD with MND (FTD/MND), the authors compared the glucose metabolism of 8 patients with FTD/MND with that of 29 patients with FTD. All of the patients with FTD/MND showed glucose hypometabolism only in the frontal area, whereas most patients with FTD had hypometabolism in the frontal and temporal areas. FTD/MND also showed a more symmetric pattern of glucose hypometabolism than FTD.