The authors present a case of refractory multiple myeloma in an elderly patient with heterozygosity for the G20210A mutation of factor II and for the C677T mutation of methylenetetrahydrofolate reductase. This patient developed acute, multiple cerebral infarctions 5 months into the treatment with thalidomide. The patient improved on oral anticoagulation. The authors presume that thalidomide increased the risk of cerebral infarction in this predisposed patient. The presence of increased risk for thrombosis should alert clinicians to screen patients presenting with systemic thrombosis for inherited thrombophilia. This risk increases with the presence of diseases and therapies that predispose for a hypercoagulable state. They suggest that patients required to be on thalidomide should be screened for inherited thrombophilia and should be considered for prophylactic anticoagulation therapy.