We report a rare case of adult varicella complicated by marked thrombocytopenia. A 49-year-old woman presented with fever and rash for 3 days. Blood examination revealed marked thrombocytopenia (2.7 × 10(4)/μL). Varicella infection was diagnosed after elevated levels of varicella zoster virus IgM and IgG antibodies were observed 2 weeks later. In this case, thrombocytopenia was due to varicella infection, and the mechanism was estimated to be non-immunological. Because varicella infection complicated by thrombocytopenia may result in fatal bleeding, thrombocytopenia in patients with varicella warrants close attention.