Van Wyk-Grumbach syndrome is a rare disease characterized by precocious puberty associated with prolonged hypothyroidism and multicystic enlarged ovaries. A 9-year-old girl with Down syndrome visited our hospital for early menarche. At birth, she showed subclinical hypothyroidism [11.8 μg/dL of thyroxine (T4) and 6.05 μIU/mL of thyroid stimulating hormone (TSH)], but she had not been followed up in our clinic. On physical examination, pubertal Tanner stage was breast II and pubic hair I. Laboratory findings were as follows: 0.30 ng/dL of free T4, 81.30 μIU/mL of TSH, 0.1 IU/L of luteinizing hormone, and 6.35 IU/L of follicle-stimulating hormone. Her bone age was 6 years. Her pelvic sonogram revealed multiple cysts in both enlarged ovaries. She was diagnosed with Van Wyk-Grumbach syndrome. Levothyroxine treatment at a dose of 50 mg/m2/day was started. Regression of breast development was obtained after 2 months, and her vaginal bleeding did not recur.