The cause of an eight-year-old boy’s testicular pain on one side, but the ultrasound shows normal may be related to orchitis, epididymitis and other diseases. 1. Orchitis: when the causative agent invades the testicle it is easy to cause infection and pain under the stimulation of inflammation. Secondly, if the condition is mild and no swelling occurs, then the ultrasound test may show normal. 2. Epididymitis: Epididymitis is a common male genital disease, mostly caused by infection with Enterobacteriaceae. At the onset of the disease, localized pain and ultrasound shows normal. It is important to note that since there are many medications available to treat this symptom, it is important to follow the doctor’s instructions to use the medication, and not to use the medication privately to avoid serious adverse reactions.