We describe here an adult case of varicella-associated idiopathic thrombocytopenic purpura (ITP). A 23-year-old Japanese male presented with generalized hemorrhagic vesicles and fever. Laboratory examinations revealed severe thrombocytopenia associated with anti-platelet IgG auto-antibody. The patient rapidly recovered within a few days after antiviral agent (vidarabine) administration, and the platelet count returned to normal with skin lesion improvement. Idiopathic thrombocytopenic purpura associated with viral infection in adulthood is relatively rare.