Horses commonly suffer from respiratory diseases associated with excess secretions in the airway lumen, some of which are presumably derived from airway mucous glands. However, these structures have been little investigated in the horse. Accordingly, we describe here the number, distribution and size of equine tracheal mucous glands, and compare the data with similar information for other mammalian species. Two types of gland acini were present. In the thick connective tissue, up to 400 μm beneath the epithelium, gland acini were grouped in thin sheets that, in cross‐section, averaged 20 μm thick and were up to 4.0 mm in length. However, it is probable that most sheets had maximal diameters much less than 4.0 mm. Between 400 to 900 μm below the epithelium, the connective tissue was much more diffuse, and glands were larger and more globular. Gland volume in the ventral portion was ˜1.7 μl/cm² of mucosal surface, and ˜1.1 μl/cm² in the dorsal portion. Glands were somewhat more abundant between, rather than over, the cartilaginous rings, but the difference between the 2 locations was not marked. Mucous gland openings were small (20 μm diameter) and very unevenly distributed, generally occurring about 100 μm apart in longitudinal rows of about 5. Average frequency of openings in the ventral portions of 3 tracheas was ˜1.0/mm² of mucosal surface. The volume of individual glands was therefore ˜17 nl. Although the frequency of gland openings in the horse trachea is similar to that for the tracheas of other large mammalian species, horse tracheal gland volume was only about 15% that of the other species. Therefore, the excess ‘mucous’ secretions seen in equine recurrent airway obstruction and other respiratory diseases are unlikely to be caused by comparatively high levels of airway mucous gland secretion. Instead, they may be caused mainly by hyperplasia of the mucus‐producing cells of the surface epithelium or by vascular transudation.