Olfactory dysfunction is a common disorder, especially in elderly people. From the etiological point of view a differentiation is made between sinunasal, traumatic and non-sinunasal causes of dysosmia. Olfactory disorders are often observed in neurodegenerative diseases, especially in patients with Parkinson's disease or Alzheimer's disease. Apart from an extensive medical history important diagnostic tools are a complete ear nose and throat (ENT) examination including nasal endoscopy and olfactory testing, for example, with "sniffin' sticks". For diagnostic purposes modern imaging procedures, such as magnetic resonance imaging (MRI) are becoming more and more important. For testing children, olfactory testing needs to be adapted and depending on the etiology, olfactory training, antiphlogistic and surgical procedures are the most promising therapeutic approaches. In cases of intracranial causes of dysosmia neurosurgeons should know and respect the anatomical structures of the olfactory signal pathway, not least for the long-term prognosis.