Cancer and its treatment affect the mental state of patients as manifested by adjustment disorders. The group includes both anxiety and depressive disorders, which are variously classified according to the ICD classification system. Therefore it is suggested to include these disorders in a separate category of so-called “psychological responses to traumatic cancer-related distress.” Implementation of screening for distress (e.g. using distress thermometer) in each Cancer Center is a precondition for good cancer care. Anxiety and depressive syndromes, which require professional treatment and care, are particularly common adjustment disorders. Furthermore, cancer patients may experience so-called organic mental disorders caused by permanent or transient impairment of central nervous system (CNS) function. Disorders of consciousness (delirium) are particularly common, especially in the elderly as well as in individuals with advanced disease stages. It is a known fact that the elderly prevail among cancer patients, thus they often suffer from cognitive impairment (dementia) as well as from personality and behavioral disorders associated with CNS damage. These disorders may coexist with cancer or may be triggered by brain tumors. Cancer patients with mental disorders should be treated with caution due to possible drug interactions and other coexisting somatic disorders. Implementation of psychological support for oncological patients on a larger scale than before is also crucial.