Malignant tumours are among the strongest risk factors for venous thromboembolism. The probability scores for deep vein thrombosis and pulmonary embolism, which we use in our everyday practice, have not yet been validated in patients with cancer, which is why they should be used with caution. Prevention of thrombosis should always be implemented in patients undergoing surgery and most patients treated conservatively, which results from the application of appropriate probability scores assessing the risk of thrombosis in these patients. The prevention method should be adjusted individually depending on the characteristics of the patient and the existence of contraindications to the use of given methods, bearing in mind their availability, cost and ability to monitor the anticoagulant effect. Treatment of venous thromboembolism in patients with cancer is different from treating it in patients with no concomitant tumour. These differences relate to both the type of treatment (anticoagulant drug selection and dosage) and its duration. Low-molecular-weight heparin is the preferred form of both initial and long-term treatment, which should last at least 6 months. Both oncologists and other health care professionals working in cancer teams should make sure at each time that the patient has at least minimal knowledge about the symptoms ensuring early detection of thrombosis. Good communication with the patient considerably facilitates effective prevention and treatment.