Can you grow a third testicle?

No: No, you cannot grow a third testicle. However, you can develop a benign cyst or a tumor that may mimic a third testicle. If a "third" testicle is identified, this should be evaluated by your doctor to do appropriate testing to determine if this is a benign condition or possible malignancy.

No: Most common cause of a so-called “third testicle” is a “spermatocele” which is a cyst containing sperm fluid arising from the epididymis adjacent to the testicle. These are common with aging, benign, and generally only require treatment if bothersome. Hydroceles, varicoceles, lipomas, and inguinal hernias are other intrascrotal masses. Any mass “directly” arising from the testicle may be a tumor.