We described a 41-year-old woman with idiopathic, symmetrical, non-arteriosclerotic, intracerebral calcification (Fahr's disease), associated with multiple myeloma. CT scans revealed severe calcification in the basal ganglia, floors of cortices, subcortical white matter, brainstem and cerebellum without calcification in the spinal cord. Cerebral angiography showed no evidence of arteriosclerosis. The cerebral blood flow measured by SPECT, parathyroid function and calcium metabolism were within normal range. The initial symptom was dystonia and spasticity in the left leg, when she was 30 years old, followed by gait disturbance, speech impairment, micrographia and dementia. M-proteinemia was pointed out when she 32 years old. M-proteinemia, which was due to primary benign monoclonal immunoglobulinemia (PBMI), made progress slowly, followed by multiple myeloma when she was 40 years old. Periodical CT scans revealed that the intracerebral calcification had worsened gradually through 8 years. Neurological abnormality had also progressed slowly. In literature, there has not been any report about Fahr's disease associated with PBMI and multiple myeloma. Our present study is the first to radiologically prove that the intracerebral calcification in Fahr's disease progresses gradually through its course.