Tracheas were removed from 8 average-sized (13 to 19 kg) dogs, 12 toy breed dogs, and 6 toy breed dogs with collapsed trachea. The tracheal arcs were counted whenever possible and measurements of the inner ventrodorsal and lateral diameters, lumen areas, cartilage and muscle thicknesses, and numbers of chondrocytes and muscle cells/0.1 mm2 were obtained from 3 regions. The regions were the 3rd ring caudal to the larynx, the region at the thoracic inlet, and the 2nd ring cranial to the carina. The 3 tracheal regions were compared with one another for all the variables in the 3 dog groups. All groups exhibited similar significant regional variations for tracheal diameters, lumen areas, and cartilage and muscle thicknesses. There were no significant differences between regions for chondrocyte and muscle cell counts. In the comparison of average dogs and normal toy breed dogs, the former had larger ventrodorsal tracheal diameters, lumen areas, and cartilage and muscle thicknesses. The measurements from the toy breed dogs with collapsed tracheas were smaller than those from the normal toy breed dogs. There were no significant differences in chondrocyte and muscle cell counts between average dogs and normal toy breed dogs.