Cerebrotendinous xanthomatosis (CTX) is a rare genetic disease caused by a deficiency of enzymes for the synthesis of bile acid, resulting in the accumulation of cholestanol with reduced chenodeoxycholic acid (CDCA) production and causing various symptoms such as chronic diarrhea in infancy, juvenile cataracts in childhood, tendon xanthomas in adolescence and young adulthood, and progressive neurologic dysfunction in adulthood. Because oral CDCA replacement therapy can effectively prevent disease progression, early diagnosis and treatment are critical in CTX. This study reports the case of CTX in a 10-year-old male who presented with Achilles tendon xanthoma and mild intellectual disability. Biochemical testing showed normal cholesterol and sitosterol levels but elevated cholestanol levels. Genetic testing showed compound heterozygous variants of CYP27A1, c.379C>T (p.Arg127Trp), and c.1214G>A (p.Arg405Gln), which confirmed the diagnosis of CTX. The patient had neither cataracts nor other focal neurologic deficits and showed no abnormalities on brain imaging. The patient received oral CDCA replacement therapy without any adverse effects; thereafter, the cholestanol level decreased and no disease progression was noted. The diagnostic possibility of CTX should be considered in patients with tendon xanthoma and normolipidemic conditions to prevent neurological deterioration.