Cryptorchidism is a condition in which the testicle is no longer in the scrotum, including testicular confirmation, testicular ectopic and undescended or incomplete testicular descent. To recognize the pathogenesis of cryptorchidism, we must first understand the physiological testicular descent during the embryonic period. At the end of embryonic week 6, the primordial germ cells move from the amnion along the mesentery of the hindgut to the gonadal bulge, and the lead band extends from the gonadal bulge toward the gonadal bulge that will become the scrotum. At embryonic week 7, the primitive gonads differentiate to form testicular tissue due to the presence of the Y chromosome SRY gene, and at week 8 a portion of the peritoneum protrudes ventrally toward the testicular introitus to become the peritoneal sphincter. During embryonic weeks 10-20, the male gonads and external genitalia develop, the testicular lead becomes hypertrophic, and the testis descends to the medial aspect of the internal ring, and remains in the same position for several months thereafter. At 30 weeks of embryonic life, the testicular introitus with the distended sphincter rapidly extends to the base of the scrotum, drawing the testis toward the base of the scrotum. The sphincter is atretic proximally. If there is no atresia, a hernia or syringomyelia may form. Understanding the physiological descent process of the testis, it is easy to understand its pathogenesis; 1. abnormal development of the testicular lead, 2. mechanical disorders such as abnormal inguinal canal and hernia, 3. abnormal attachment of the epididymis, 4. endocrine abnormalities, and 5. abnormalities of the testis itself. The incidence of cryptorchidism in newborns is related to the weight, and the incidence in mature children is 3.4%, while the incidence in those weighing less than 2500 grams is about 30%, and the incidence in those weighing less than 1800 grams is 60%. Testicular drop after birth almost always occurs within 3 months, presumably related to the physiological rise of blood testosterone during this period. The classification of cryptorchidism is divided into palpable and non-palpable. Palpable includes the scrotal root, the inferior inguinal segment and the ectopic testis; non-palpable includes the superior inguinal canal and the intra-abdominal testis. Depending on the location of the testes, the choice of our surgical method is different. For palpable testes, we can choose to make a minimally invasive incision through the groin or scrotum; for high cryptorchidism, laparoscopic exploration and surgery are required. Why must cryptorchidism be operated and what is the best age for surgery? This is the most important question for parents. It is not difficult to understand the comorbidities of cryptorchidism. 1.Cryptorchidism is mostly combined with hernia or syringomyelia, if the impaction compresses the spermatic cord blood vessels, the testicle will be further atrophied, which will lead to testicular infarction in serious cases. 2.Torsion of cryptorchidism, the chance of torsion of the undescended testicle is 21-53 times higher than that of the testicle in the scrotum. 3.Testicle injury, cryptorchidism is not as protected as the scrotum in the scrotum by the cushion of the scrotum, so it is easily damaged by external force. 4.Testicle malignancy . 4. Testicular malignancy The malignancy rate of cryptorchidism is 18-40 times higher than that of normal testis, and the high cryptorchidism is 6 times higher than that of the low one. 5. The higher the infertility position and the older the age, the more serious the changes of spermatogenic tubules, so it is recommended to operate early after 4 months for children with high cryptorchidism. The objectives of cryptorchidism treatment are 1. to reduce the psychological and mental trauma of the affected child; 2. the tendency of malignant changes can be easily detected in time; 3. the fertility may be improved; 4. to reduce or stop the further degeneration of testicular tissue. The efficacy of hormone treatment is not very precise, usually between 6-10 months after birth, mostly for children with low-level cryptorchidism. At present, most hospitals adopt surgical treatment, and the best age for surgery is around one year old, and the surgical method has been introduced in the previous article.