Epididymitis and orchitis normally co-exist with isolated epididymitis being more common than an isolated orchitis. Sexually transmitted infection is the most common cause in younger men and urinary tract pathogens are the more common culprits in older men. The most common pathogens in the under 35s are N. gonorrhoeae and C. trachomatis and E. coli is the most common cause of acute epididymitis in the over 35s. Acute testicular torsion is the most important differential diagnosis of acute testicular pain especially in younger men. If there is any suspicion of testicular torsion, the patient should be referred to secondary care immediately as surgery is required within four to six hours.