After the oncological diagnosis, smoking has a major impact on survival, course and effectiveness of oncology treatment, and quality of the further life. Smoking worsens surgery outcomes, reduces the effectiveness of radiation therapy and chemotherapy, increases the risk of side effects of oncology treatment, and increases the incidence of tumor duplication or other comorbidities like venous thrombosis, cardiovascular diseases or infections. The article contains a summary of practical recommendations for oncology patients, including smoke-free environments, the importance of zero exposure to tobacco smoke, clear advice to stop smoking to smokers and offer of tobacco dependence treatment. Except of brief intervention within few tens of seconds up to 10 minutes, intensive treatment should be available, for example in special tobacco-dependence centers. In the documentation smoking status should be recorded including exposure to passive smoking, interventions to smokers (both active and passive) should be empathically repeated. The motivation to treat tobacco dependence should be mainly related to their specific oncological diagnosis, prognosis, course and effectiveness of its treatment. Treatment of tobacco dependence should be an obvious part of quality oncological care by doctors and nurses in intensity according to their time availability. Keywords: tobacco smoking, smoking cessation, nicotine dependence, chemotherapy, pharmacological interactions, adverse effects, cancer.