BACKGROUND Disturbances of smell and taste are common. About 5% of the general population have anosmia (absence of the sense of smell). Olfactory dysfunction can markedly impair the quality of life. METHODS Review of pertinent literature retrieved by a selective search. RESULTS In recent years, simple and reliable tests of the sense of smell have been introduced in otorhinolaryngology. Olfactory testing has become a new focus of attention in neurology as well, mainly because many patients with neurodegenerative diseases-including the majority of those with Parkinson's or Alzheimer's disease-have olfactory loss early on in the course of their disorder. Olfactory dysfunction is thus regarded as an early sign of neurodegenerative disease that may allow a tentative diagnosis to be made years before the motor or cognitive disturbances become evident. As for the treatment of olfactory loss, anti-inflammatory drugs and surgery can help in some cases, and olfactory training can lead to significant improvement of post-viral olfactory deficits. CONCLUSION Olfactory dysfunction is common and becomes more common with advancing age. It is increasingly receiving attention as an important sign for the early diagnosis and the differential diagnosis of neurodegenerative disorders.