We present a young woman who was diagnosed as primary antiphospholipid syndrome (deep vein thrombosis and pulmonary embolism in 1999; moderate thrombocytopenia with high-positive anticardiolipin ELISA tests in 2002, and cerebral thrombosis in 2003), and then developed hairy cell leukemia (massive splenomeaaly, neutropenia, hairy cells in blood smear and bone marrow trephine biopsy in 2004). A partial remission was achieved with interferon-alpha 2a therapy. After the initiation of 2-chloro-deoxyadeno sine therapy, splenomegaly disappeared, the percentage of hairy cells on the bone marrow reduced below 1%, platelet count returned to normal levels. After complete remission was achieved for hairy cell leukemia proved by bone marrow trephine biopsy, antiphospholipid antibodies were found to be negative, and no further thromboembolic complications and thrombocytopenia were seen. In our literature search, we found only six cases that had both antiphospholipid antibodies and hairy cell leukemia. Our case is the first case of antiphospholipid syndrome before the development of hairy cell leukemia. Both hairy cell leukemia and anti phospholipid syndrome responded to lymphocytotoxic treatment with 2-chloro-deoxyadenosine.