The pineal organs of 10 species of tinamid birds belonging to the genera Crypturellus, Nothura, Rhynchotus and Tinamus were studied in serial microscopic sections of the entire medial region of the brain. All were located in a triangular space formed by the cerebral hemispheres and the cerebellum. They have the form of a club with the enlarged distal part enclosed in the dura-mater. In all species the pineal is formed of tubulofollicular structures, the walls of which are covered by a pseudo-stratified epithelium with elongated cells. In Rhynchotus and Nothura there is a predominance of small follicles with a reduced lumen and a regular outline, whereas in Tinamus and Crypturellus there is a predominance of large follicles with a wide lumen and an irregular outline. Our results show that morphological organization of the pineal organs in tinamids is similar to that observed for the majority of modern birds, in spite of the fact that they are generally regarded as very primitive.