Development of the penis of wild-type and androgen-insensitive (Tfm) mice was compared histologically to demonstrate possible androgen-dependent histogenesis in this organ. The os penis of the normal males consists of a hyaline cartilage and a membrane bone in the proximal segment and a fibrocartilage in the distal segment. Only the membrane bone of the proximal segment developed in the Tfm mice. The corpus cavernosum penis, corpus cavernosum glandis, and corpus cavernosum urethrae developed only to a small degree in the penis of the Tfm mice. It is also suggested that the morphogenesis of the urethra and formation of spines on the skin of the glans penis are dependent on androgens.