A 37-year-old male with cerebrotendinous xanthomatosis showed brain abnormal MRI findings and osteoporosis. His parents had no similar symptoms. He had mental retardation since childhood. Swelling of Achilles tendons was noticed at age 28, and gait disturbance appeared at age 34. Physical examination revealed bilateral cataracts and swelling of Achilles tendons. Neurologically, he showed mental retardation, cerebellar ataxia and spastic tetraparesis. Cerebrotendinous xanthomatosis was diagnosed by marked elevations of serum cholestanol level (24.3 micrograms/ml) and cholestanol/cholesterol ratio (1.81%) as well as characteristic clinical manifestations. On brain MRI study, T2-weighted sequence showed bilateral focal lesions with high intensity signal in the globus pallidus and cerebellar white matter adjacent to the dentate nucleus, and T1-weighted sequence showed low to iso-intensity signal in the same regions. These findings suggested demyelination rather than xanthoma or lipid infiltration. Radiological examination showed mild osteoporosis of lumbar bone. However, serum levels of vitamin D3 and calcitonin were within normal range, and renal function was normal. Osteoporosis in this patient possibly resulted from disuse bone atrophy for several years. The combination therapy of oral administration of chenodeoxycholic acid and HMG-CoA reductase inhibitor (pravastatin), and LDL apheresis slightly improved EEG abnormality and gait disturbance, but not brain MRI abnormality.