BACKGROUND: The association between Down syndrome (DS) and hyperuricemia has been described for a long time. The cut-off points for hyperuricemia should be determined as the upper limits of the uric acid (UA) level according to age- and gender-specific reference UA values prepared for children with DS. METHODS: This study included 238 children (140 males and 98 females) with DS, below 21 years of age, who visited our medical center from May 1991 to June 31, 2018. Laboratory data were used to calculate the reference UA levels according to age and gender. We also inquired about the relationship between hyperuricemia and the presence of other diseases and other laboratory findings in children with DS. Fourteen patients had already been definitively diagnosed and treated. The UA data from these cases were excluded from the analysis. RESULTS: The UA levels were significantly higher in all age groups among individuals with DS in comparison with the general population. Newly established reference values revealed 55 patients with hyperuricemia. The prevalence of hyperuricemia in males and females was 25.0% (35/140) and 20.4% (20/98), respectively. The number of hyperuricemia cases increased rapidly after 10 years of age. The UA levels were closely correlated with hemoglobin (Hb) values, creatinine, and total bilirubin, which are closely associated with dehydration in children with DS. CONCLUSIONS: These reference levels could help to evaluate hyperuricemia candidates who should be carefully monitored and treated with uric-acid-lowering drugs in the future.