A Yorkshire terrier and a Chihuahua were referred for acute onset, generalized tonic-clonic seizures and were suspected to have meningoencephalitis based on magnetic resonance (MR) imaging findings. Brain lesions appeared hyperintense with T2-weighted imaging and hypointense with T1-weighted imaging, and were characteristic of necrotizing meningoencephalitis. Both dogs were diagnosed with necrotizing meningoencephalitis based on pathologic findings. Fluorine-18 fluorodeoxyglucose positron emission tomography (FDG-PET) was performed on both animals before euthanasia with the permission of the owner. In FDG-PET images, these lesions seen in MR images were characterized by multifocal or diffuse hypometabolism. Our FDG-PET results provided evidence of glucose hypometabolism in areas of necrosis and cavitation associated with necrotizing meningoencephalitis. FDG-PET has the potential to provide valuable diagnostic information in dogs with suspected necrotizing encephalitis.