Acute orchitis mostly occurs in patients with urethritis, cystitis, prostatitis, post-prostatectomy and long-term indwelling catheter. Infection spreads to the epididymis via lymph or vas deferens causing epididymitis. The common causative organisms are Escherichia coli, Proteus mirabilis, Staphylococcus and Pseudomonas aeruginosa. Bacteria can spread to the testis via the bloodstream and cause simple orchitis. However, the testes are rich in blood flow and have a strong resistance to infection, so this is less common. Mumps orchitis needs to be highlighted here. Mumps is the most common cause of orchitis and is most often seen in men in late adolescence. It is caused by bloodstream invasion of the testes by the mumps virus. About 12-20% of mumps patients have orchitis as a complication. The onset of mumps-induced orchitis is rapid, usually appearing 3-4 days after the onset of mumps. The scrotum is erythematous and edematous. Unlike epididymitis, there are no urinary symptoms, and there may be significant deficiency when the temperature reaches 40°C. On examination, mumps or other foci of infection may be detected, and one or both testicles are enlarged and highly painful. The scrotal skin is red and the transillumination test is positive if there is an acute syringomyelia. In these patients, blood leukocytes are elevated, urinalysis is generally normal, sometimes with protein or microscopic hematuria, and pathogenic viruses may be found in the urine during the acute phase. The clinical diagnosis is mainly based on symptoms such as high fever, chills, swollen and painful testicles, redness and edema of the scrotum, etc. Of course, it should be distinguished from acute epididymitis, mumps orchitis, spermatic cord torsion and incarcerated hernia. Early diagnosis, timely antibacterial and anti-inflammatory treatment, and removal of the cause of the disease are important means to protect good function in the future. Patients are advised to rest in bed, hold the scrotum high, apply local heat and physiotherapy. In case of obvious pain, closed injection of 1% lidocaine to the spermatic cord can be given to reduce pain. For those with abscess formation, incision and drainage should be performed. For patients with mumps orchitis, antiviral therapy, as well as serum injections, gammaglobulin, and hormones should also be given during the mumps recovery period. In a small number of patients with orchitis, after cure, due to fibrosis and damage to the spermatogenic tubules, testicular atrophy can cause sterility, but does not affect the development of secondary sexual characteristics and sexual function.