A 35-year-old white male with symptoms of paranoid schizophrenia was treated by psychiatrists for 13 years. During the final year, he developed severe dysphagia, reduced strength of the upper extremity muscles, and cognitive dysfunction. The patient died in his sleep. The only pathology found in coronal brain sections was ill-defined periventricular foci with prominent, firm vessels. Microscopy revealed abundant, hematoxylin and eosin-eosinophilic, periodic acid-Schiff-positive, thioflavin T-positive, and Congo red-negative deposits in the vessel walls, with hypoxic encephalopathy in the affected regions. Immunohistochemistry showed lambda light chains as the main component of the deposits. Ultrastructural analysis showed amorphous electron dense material in the vessel walls. Perivascular B-cell proliferation was present in the vicinity of affected areas. Polymerase chain reaction was applied for the assessment of B-cell clonality, revealing monoclonal rearrangement of the heavy chain Ig gene. Neither in the kidney nor in any other organ were deposits detected. This is the first case report of light chain deposition disease restricted to the brain.