Allergic contact dermatitis caused by acyclovir is rare but can occur. In patients with such dermatitis from this antiviral drug, oral acyclovir can cause a systemic cutaneous adverse drug reaction. Also, in these patients, valacyclovir and famciclovir could cause same systemic cutaneous reaction and it has been probably thought due to their common chemical structure (2-aminopurine nucleus). We report systemic valaciclovir reaction subsequent to acyclovir contact dermatitis. 30-year-old woman has been used acyclovir ointment due to recurrent H. simplex on lip. Several months ago, she had a lip dermatitis after application of acyclovir ointment. 2 days ago, she was presented multiple erythematous confluent maculopatch on trunk after oral valacyclovir. Patch tests were performed with valacyclovir(tablet), acyclovir (tablet), famciclovir(tablet), motillium(tablet), vaselline, acyclovir ointment. Patch tests were negative but oral administration of acyclovir, famciclovir, valaciclovir caused itchy erythematous maculopatch on the trunk, lip. Common chemical structure (2-aminopurine nucleus) is probably thought to provokes both contac allergy and systemic reactions. Foscarnet and cidofovir could be alternative drugs because of not having this core. Herein we report systemic valacyclovir reaction subsequent to acyclovir contact dermatitis.