Guidelines for the prevention and treatment of venous thromboembolism (VTE) are aimed to improve patients’ safety and quality of life by appropriate prophylaxis and treatment of deep venous thrombosis (DVT) and pulmonary embolism (PE). These guidelines relate to adult cancer patients treated non-surgically. Recommendations included in those guidelines do not relate to paediatric patients. The guidelines presented here directed to physicians and other healthcare professionals taking care of mentioned patients: clinical oncologists, haematologists, radiotherapists, pulmonologists, oncological gynaecologists, internal medicine physicians, and GPs. Venous thromboembolism (VTE) comprises a serious problem in oncology because it is the most common complication as well as the second most common cause of cancer-related deaths. The term “venous thromboembolism” includes the cases of DVT and PE; however, the former is a primary event and the latter is a secondary result. Active malignant disease classifies patients to a group with at least moderate risk of VTE. D-dimer levels could be increased in cancer patients without concomitant VTE. D-dimer levels below cut-off value (negative D-dimer) do not exclude VTE in cancer patients. In patients with active malignant disease with clinical symptoms suggesting VTE ultrasound (US) examination of deep veins or computed tomography angiography (angio-CT) should be performed, depending on the symptoms. Low-molecular-weight heparins (LMWH) are the drugs of choice in prevention and treatment of VTE in cancer patients. Antithrombotic treatment in cancer patients with DVT does not differ from treatment of cancer patients with PE, except clear indications to thrombolytic therapy. Cancer patients with clinical symptoms suggesting PE (dyspnoea, chest pain or tachycardia) are per definition classified into the group of moderate or high clinical probability of PE. The majority of PE cases account for embolism, which do not warrant thrombolytic treatment and should be treated with LMWH, UFH, or fondaparinux; LMWHs are the treatment of choice in cancer patients with VTE. Cancer patients have increased risk of recurrence of VTE. Available evidence does not justify the use of antithrombotic drugs to prolong survival in cancer patients.