Infection and inflammation of the male reproductive tract are accepted as important aetiological factors of infertility. With regard to their impact on male reproductive function, orchitis and epididymo-orchitis due to local or systemic infection as well as noninfectious aetiological factors are of particular concern. There is clinical and pathological evidence that chronic inflammatory conditions of the testes can disrupt spermatogenesis and irreversibly alter both sperm number and quality. In the majority of patients, however, diagnosis is hampered by an asymptomatic course of the disease and unspecific clinical signs. Hence, respective epidemiological data are scarce. On the other hand, systematic histopathological work-up of testicular biopsies from infertile men indicates a high prevalence of inflammatory reactions. A characteristic pattern of inflammatory lesions with focal or multifocal, predominantly peritubular lymphocyte infiltration and concomitant damage of seminiferous tubules is seen in chronic orchitis of various origins. This supports the concept that induction of testicular inflammation is associated with a T-cell-mediated autoimmune response, i.e. disruption of the immune privilege. Moreover, despite the patchy distribution of the lesions, testicular volume and score counts for spermatogenesis may be significantly reduced. In conclusion, asymptomatic inflammatory reactions in the testis should not be neglected as an underlying cause or co-factor of male infertility. However, definitive diagnosis of chronic asymptomatic orchitis still requires testicular biopsy and guidelines for the therapeutic management are not yet available.