Derangements of hemostasis and hemocoagulation in patients with malignancies are known as paraneoplastic syndrome. Their origin, however, has not been unequivocally established and explained, and data on their occurrence are controversial. Examination of 157 patients with different malignant tumor diseases yielded pathological laboratory findings in 94.2%. The most frequent finding was the state of hypercoagulation in 41.0%; hypercompensated syndrome of disseminated intravascular blood clotting (DIC) was found in 10.9%, compensated DIC syndrome in 18.0%, consumptive coagulopathy in 3.8%, and in 19.2% hypocoagulation state caused by other abnormalities. The laboratory finding was normal only in 5.8% of the patients. In the light of the high occurrence rate of hemostatic and hemocoagulation changes in malignant diseases, established by laboratory analysis, the use of anticoagulants and antiaggregation substances appears to be justified in the majority of cases, both to prevent the development of these changes which may complicate the course of the malignant condition, and in preoperative care to reduce the rate of postoperative thromboses in patients with tumors.