Mumps can occasionally affect the testicles, giving rise to a condition called orchitis, which means inflammation of the testicle. Orchitis in adult (post-puberty) males can result in atrophy of the testicles, which in turn can impair sperm production. However, complete sterility is rare in adult males that develop orchitis. Both testicles have to be affected by orchitis in order for fertility to be threatened. It is estimated that 30% of adult males who develop mumps also develop orchitis during the course of the illness. In a third of these, cases both testicles are affected.
If orchitis occurs before puberty, fertility is usually unaffected.
