Post-infectious encephalitis is a rare manifestation of mumps. We report the case of an 11-year-old boy who presented with pseudobulbar syndrome and parkinsonism, 1 week following mumps parotitis. Magnetic resonance imaging of the brain showed bilateral and symmetric changes in the basal ganglia with signal abnormalities in the white matter surrounding the lentiform nuclei. Lumbar puncture confirmed the presence of mumps antibodies in the cerebrospinal fluid, confirming the diagnosis of post-mumps encephalitis. Symmetric basal ganglia involvement has been described in mumps encephalitis. However, to our knowledge, this is the first reported case with basal ganglia lesions surrounded by white matter abnormalities, the so-called lentiform fork sign, commonly found in cases of metabolic acidosis.