Radiology is an important diagnostic instrument in avian medicine, but standard measurement ranges for the objective evaluation of radiographs are rare. During the setup of a medical management program for the critically endangered Spix’s macaw (Cyanopsitta spixii), we measured selected internal organs of the coelomic cavity on 29 radiographs, taken under standardised conditions, of fully grown and juvenile, clinically healthy animals. Thus, reference ranges were established for the radiographic silhouettes of the heart, liver, kidneys, spleen, proventriculus, and the keel of the sternum. The 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 width of heart to width of liver). There were no significant differences between the sexes among the fully grown birds. Compared to the fully grown birds, juvenile females had significantly larger heart width (19.8 ± 1.4 cm versus 21.2 ± 0.7 cm), larger ratio of the heart width to thorax width (0.86 ± 0.08 versus 0.94 ± 0.09), and larger horizontal width of the spleen (7.7 ± 0.6 cm versus 8.5 ± 0.4 cm). Comparison of the results with published data, revealed that Spix’s macaws have comparable radiographic measurements to other psittacine birds. These reference ranges will facilitate a more objective radiographic evaluation of captive Spix’s macaws.