Because of their important physiological functions, the avian air sacs have already been described in detail.However, three-dimensional illustrations, which are very useful for clinical research and in particular for medicalimaging, are sparse. Therefore, in the present study the air sac system of young chickens was visualized using thecorrosion casting technique. The 9 air sacs that could be demonstrated were the unpaired clavicular air sac and thepaired cervical, cranial and caudal thoracic, and abdominal air sacs. The latter were by far the largest and wereinterwoven with the abdominal organs. The numerous diverticles extending from the air sacs were rather small. Thismight be the result of the applied technique or the fact that the air sac system has not yet been fully developed in youngbirds. Further studies investigating potential species differences or conformational changes of the air sacs in growinganimals are valuable.