Herpes simplex viruses are common worldwide. Their genome comprises linear double-stranded DNA. They are characterized by the ability to spread rapidly, cytotoxicity and the capacity to remain in latency. Infection is usually asymptomatic. Primary or secondary infection can, however, cause ulcerative and vesicular lesions on the skin, keratoconjunctivitis, disseminated infection, encephalomeningitis. The virus is especially dangerous for pregnant women, newborns and immunocompromised hosts. The basic medicine used in prevention and therapy is acyclovir. It displays very good efficacy if administered at initial stages of the disease and if the duration of therapy and dosage of the drug are suitable.