Too small testicles may be due to congenital testicular hypoplasia, cryptorchidism and other diseases. 1. Congenital testicular hypoplasia: It is usually caused by the non-separation of sex chromosomes during the maturation and division of the egg. Patients usually have no abnormality in childhood, and the abnormality may appear in puberty or adulthood. The patients can be manifested as long and thin lower limbs, scanty pubic hair or beard, short penis, significant reduction of testicles on both sides, etc. Some of the patients can also be accompanied by hypertrophy of breasts on both sides, and no spermatozoa in semen. 2. Cryptorchidism: this disease is a congenital disease with genetic tendency, the cause of which is still unclear, and it is mostly considered to be related to abnormal function of the traction belt between testis and scrotum, mechanical obstruction, vascular abnormality of the spermatic cord, abnormal development of testis, abnormal testicular structure, and hereditary and other factors. Patients usually have no conscious symptoms, and most of them will show poor scrotal development, scrotal emptiness, etc. Some patients can also touch the testis in the groin or outside the scrotum, which is relatively small compared with the normal testis, and only a localized bulge can be seen. Some chromosomal abnormalities and delayed pubertal development may also lead to too small testicles. It is recommended that patients should consult a doctor in time to find out the cause of the disease and then treat the disease actively when they find that their testicles are too small.