Serum soluble thrombomodulin is known to be a factor in visceral vascular disorders such as organic vasculitis in collagen diseases, but recently it has also been reported as a predictor of thrombotic crisis in thrombotic diseases. In this report, serum soluble thrombomodulin levels and events of thrombotic crises in clinical patients were studied retrospectively in our dermatology department over the past five years. I found an increase in soluble thrombomodulin one to two months before the crisis in eight of ten patients including three with anti-phospholipid syndrome, two with lupus anticoagulant-positive systemic lupus erythematosus, four patients with chronic disseminated intravascular coagulation syndrome and one patient with thrombotic thrombocytopenic purpura. A decrease was found after treatment. Other tested parameters did not respond as soluble thrombomodulin, and they were not useful for predicting the crisis one to two months before the crisis. These results suggest the possibility that soluble thrombomodulin might be an important factor in predicting thrombotic crisis.