Background The aim of this study was to verify the accuracy of anthropometric equations to estimate the body density (BD) of adults with Down syndrome (DS), and propose new regression equations. Materials and methods Twenty‐one males (30.5 ± 9.4 years) and 17 females (27.3 ± 7.7 years) with DS participated in this study. The reference method for BD was air displacement plethysmography (ADP). Also, the BD was estimated by anthropometric equations. The body fat percentage (BF %) was estimated by the Siri equation. Results For females, the Durnin and Womersley equation showed no difference from the ADP, but a trend of underestimation was observed. For males, all equations were significantly different for the BF % from ADP. The equations developed in this study showed a high correlation and acceptable agreement with BF % from ADP in both genders. Conclusion All equations are not valid for DS adults. The new equations developed here were accurate in estimating the BF %.