Juvenile Huntington disease manifests differently from adult Huntington disease and has more variability in presentation. We describe a child with cognitive decline and adventitial movements in whom Huntington disease was confirmed with genetic testing. MR imaging showed abnormal T2 prolongation in the putamina and progressive caudate atrophy, and MR spectroscopy revealed elevated myoinositol and diminished N-acetyl aspartate, creatine, and phosphocreatine. Imaging findings of caudate atrophy and abnormal T2 prolongation in the putamina with MR spectroscopy findings consistent with dense gliosis can be helpful indicators of juvenile Huntington disease.