A 21-year-old man with a history of sudden rectal hemorrhage was referred to our hospital. Examination disclosed thrombocytopenia and hepatosplenomegaly. A liver biopsy specimen demonstrated Gaucher cells in Glisson's capsule. Additional investigations revealed a low level of leukocyte β-glucosidase activity and common mutations of the glucocerebrosidase gene, L444P/D409H. We diagnosed the patient with Gaucher disease type 1. He underwent enzyme replacement therapy. Thrombocytopenia and hepatosplenomegaly improved at a rate of approximately 50 and 20%, respectively, within 6 months. This case suggests that we must pay attention to adult Gaucher disease as a differential diagnosis for cryptogenic thrombocytopenia.