Van Wyk-Grumbach syndrome is a rare cause of precocious puberty due to hypothyroidism. We report a case of Van Wyk-Grumbach syndrome in a 4.3-year-old female patient with Down syndrome. She was investigated for hematuria for three months before she was referred to our clinic. Physical examination revealed typical morphologic features of Down syndrome and hypothyroidism. Pubertal development stages were: breast at stage III and pubic hair at stage I. In luteinizing hormone releasing hormone (LHRH) stimulation test, peak LH level remained less than 0.1 mIU/ml. Serum estradiol level was 117.7 pg/ml, which was higher than normal for her age (normal range: 2-15 pg/ml). The pelvic ultrasonographic evaluation revealed bilateral multicystic enlarged ovaries. Serum thyroid stimulating hormone (TSH) concentration was higher than 500 microIU/ml and free thyroxin (FT4) and free triiodothyronine (FT3) levels were as low as 0.4 ng/dl (0.7-1.48) and 1.0 pg/ml (1.71-3.71), respectively. L-thyroxin treatment at a dose of 100 microg/m2/day was started. Regression in breast development was obtained after one month and her bleeding did not repeat again. In conclusion, urinary and vaginal bleeding in young children must be clearly differentiated, and hypothyroidism must be investigated in children who have precocious puberty.