The epidemiology of herpes simplex virus (HSV) infections describes: the clinical picture varying from subclinical to severe in various age groups, latency and recurrent infections, the transmission through direct contact related to the localisation of the lesions (ano-uro-genital for HSV2, oro-labial for HSV1), the world wide human reservoir, the lack of seasonal peak of incidence and the exceptional limited outbreaks. Serological and virological tests used for evaluating the frequency of acquired infections and the prevalence of various clinical and epidemiological aspects of herpetic infections have greatly changed in the last decade: (a) specific serological tests differentiate anti HSV1 and anti HSV2 antibody, allow the precise measurement of HVS1 and HSV2 infections prevalence and demonstrate the increasing frequency of Herpes Simplex genital infections in the last decades, in most of the countries (but Japan), (b) the development of direct diagnostic tests: virus growth in cells cultures, antigens detection by immuno-fluorescence and ELISA tests, genome amplification and detection by PCR and hybridization pointed but that: (1) the asymptomatic genital HSV excretion represents a frequent risk for neonatal contamination, (2) genital HSV1 noticeably increased in frequency, its epidemiological consequences are not yet evaluated, (3) a severely compromised immune status favours the frequency, the severity and chronicity of HSV infections, and the selection of antiviral resistant strains. The large use of acyclovir and derivatives in treatment and prophylaxis of HSV infections deeply modified the evolution, prognosis and management of HSV infections, but stressed the need for a survey of acyclovir resistant strains in immuno-competent and immuno-compromised patients.