Radiology is an important diagnostic instrument in avian medicine, but standard measurement ranges for the objective evaluation of radiographs of birds are rare. To establish radiographic reference ranges for the critically endangered Spix's macaw (Cyanopsitta spixii), we measured radiographic silhouettes of the heart, liver, kidneys, spleen, proventriculus, and keel of the sternum on 29 radiographs taken under standardized conditions in adult and juvenile, clinically healthy birds. Ratios were determined for the proventricular diameter-to-keel height, the width of the heart to the width of the thorax, and for the “hourglass shape” (ratio of the width of the heart to the width of the liver). No significant differences were found between the sexes among the adult birds. Compared with adult birds, juvenile females had a significantly larger heart width (19.8 ± 1.4 mm versus 21.2 ± 0.7 mm), ratio of the heart width to the thorax width (0.86 ± 0.08 versus 0.94 ± 0.09), and horizontal width of the spleen (7.7 ± 0.6 mm versus 8.5 ± 0.4 mm). Results of radiographic measurements in the Spix's macaws were comparable to those published from other psittacine species. These reference ranges will facilitate a more objective radiographic evaluation of captive Spix's macaws.