Oral acyclovir is an antiviral nucleoside analogue that has recently been released in Canada for use in selected patients with genital infections by the herpes simplex virus. First episodes of genital herpes should be treated with oral acyclovir as soon as the diagnosis is considered. Most people with recurrent genital herpes do not require systemic drug therapy. Selected patients with severe or long-lasting recurrences, recurrences associated with long prodromal periods (greater than 12 to 24 hours) or systemic complications such as erythema multiforme and eczema herpeticum may receive measurable benefit from treatment at the onset of symptoms. In most patients frequently recurrent disease can be suppressed with long-term therapy. Since long-term safety beyond 1 year has not been established, suppressive therapy should be stopped at least once per year to reassess the recurrence pattern. Acyclovir has not been adequately tested for safety in pregnancy and should not be prescribed for pregnant women unless the potential benefits outweigh the risks. Careful attention to disease severity, accurate diagnosis and exclusion of other causes of genital lesions will ensure that the drug is used only when beneficial.