We retrospectively examined the clinical features and the neuroradiological findings on autopsy of 2 cases of young-onset dementia. The patient in case 1 was a 43-year-old woman who was unable to determine the time on the clock and who made frivolous remarks. Neuropsychological test batteries demonstrated memory impairment and frontal lobe dysfunction. T2-weighted magnetic resonance imaging (MRI) of the head revealed abnormal high-intensity signals around the lateral ventricles and thinning of the corpus callosum. Single photon emission computed tomography (SPECT) revealed patchy reduction in the accumulation of tracers in both the frontal lobes. Her neurological condition gradually deteriorated, and she died 13 years after the onset of the disease. She was clinically diagnosed with atypical Alzheimer's disease on the basis of visual cognitive impairment and memory impairment observed in the initial phase. However, the neuropathological diagnosis was adult-onset leukodystrophy with axonal spheroids. The patient in case 2 was a 43-year-old man who had gradually started behaving selfishly and had become ill-tempered and apathetic. He was admitted to a hospital. He was anosognosic and showed frontal lobe dysfunction. T2-weighted MRI scan of the brain showed abnormal high-intensity signals around the lateral ventricles; atrophy of the frontal and temporal lobes, hippocampus, and brainstem; and thinning of the corpus callosum. SPECT revealed patchy reduction in the accumulation of tracers in both the frontal lobes and the cerebellum. His neurological condition gradually deteriorated, and he died after being clinically ill for 7 years. The patient was clinically diagnosed with frontotemporal dementia on the basis of the clinical features and MRI findings. However, the neuropathological diagnosis was chronic meningoencephalitis. The frequency of neurological metabolic and inflammatory diseases is significantly high although it is not as high as that of degenerative diseases in young-onset dementia. Since such diseases may respond to therapy, they should be considered in the differential diagnosis of young-onset dementia, especially in patients presenting with atypical clinical features. Neuroradiological examination may contribute to the differential diagnosis of atypical dementia at young age.