Antiphospholipid antibodies are commonly related to connective tissue disorders, the use of certain drugs, and infection. It is thought that antiphospholipid syndrome (APS) is associated primarily with connective tissue disorders. We describe a healthy young male who had an episode of APS that was associated with cytomegalovirus infection and who developed mesenteric and femoropopliteal thrombosis. He responded well to treatment with anticoagulants; 6 months after the onset of APS, IgM and IgG anticardiolipin antibody titers declined. We point out the importance of screening for infectious agents in cases of APS; if the agents are identified, APS may be transitory.