We assessed the utility of radiographic findings as aids to the diagnosis of Down syndrome (DS) in stillborn infants. The iliac index may help to confirm the diagnosis of DS in stillborn infants in whom it is suspected clinically, but in whom it cannot be confirmed cytogenetically. It also can serve as a screening procedure to select stillborns in whom fluorescent in situ hybridization of fixed tissues should be completed. An iliac index of 59 degrees differentiates between control and affected stillborns with the highest accuracy, but false positives persist above 55 degrees, and false negatives are common below 64 degrees. We recommend that a conservative cutoff value of 55 degrees be used if the radiographic data serve as the principal means of diagnosing DS in stillborn infants. A cutoff value of 64 degrees may be appropriate if the radiographic data are used to screen stillborn infants for fluorescent in situ hybridization studies.