Herpes simplex virus type 1 and type 2 cause a wide range of illnesses ranging from minor cold sores to severe necrotising encephalitis or disseminated systemic infections seen in immunocompromised patients including neonates. Following primary infection, the virus is not eradicated from the body but is latent in sensory nerve ganglia where it can reactivate and cause recurrent disease. Aciclovir is the most studied and used antiviral agent with activity against herpes simplex virus infections. In most situations the use of aciclovir shortens the duration of clinical illness and viral shedding and reduces morbidity and mortality. All life- or sight-threatening infections should be managed in an inpatient hospital setting with intravenous therapy. The use of oral aciclovir is recommended in patients with non-life-threatening illness who may still have significant symptoms.