A large and small testicle in newborns after birth is relatively common in clinical practice. Its most common causes are syringomyelia and inguinal hernia, and less common are testicular inflammation and testicular tumor. The diagnosis can be established by ultrasound. In the case of syringomyelia, follow-up observation is performed and most of them can be absorbed on their own. If it does not improve by about one and a half years of age, then consider surgery. Inguinal hernia is mainly caused by the intestinal tube protruding into the scrotum, if the hernia can slide, it is not a big problem, pay attention to avoid incarceration, and if there is incarceration, it needs to be treated in time. If it is caused by testicular inflammation, need to actively anti-infection treatment. If diagnosed as rare testicular tumor, different treatment options need to be chosen according to different types and severity. Therefore, if a newborn baby is born with a large or small testicle, ultrasound is needed in time for examination.