The testicles are large on one side and small on the other. It is recommended to go to the hospital for relevant examinations to clarify the possible causes: First, patients with orchitis may have an increase in the size of the testicles on the inflamed side, accompanied by obvious pain, and even changes such as redness of the scrotal skin and an increase in body temperature. Secondly, patients with testicular sphingomyelia can show a large testicle on one side and a small testicle on the other side, often because the scrotum is filled with fluid, so that it appears from the appearance of a large side and a small side. However, the probability of acute pain in this case is relatively low, and it shows a chronic feeling of swelling and pain, which needs to be ruled out by ultrasound examination of the scrotum. Thirdly, patients with testicular tumor may have an increase in testicular volume on the side of the tumor, accompanied by hardening of the testicle and a feeling like touching a stone when touched, accompanied by a feeling of localized swelling, which requires testicular tumor index test and CT or MRI examination of the testicle for further exclusion. Fourthly, patients with varicocele may have atrophy of the affected testicle, while the normal side of the testicle is slightly larger than the affected side, usually accompanied by a softening of the testicle, and the varicose blood vessels can be felt in the scrotum.