Although a large number of individuals experience olfactory disorders following accidents, disease states, medical interventions, aging, and exposure to environmental chemicals and pollutants, few medical practitioners have the expertise or staff to provide appropriate clinical evaluation, treatment, counseling, or referral for such patients. The present review examines studies associated with the diagnosis and treatment of olfactory disorders, as well as ones noting olfactory signs as diagnostic markers for brain tumors and other serious problems. A basic taxonomy of smell dysfunctions is presented, along with a review of etiologic factors, including local diseases and mechanical obstruction of the airways, viral infections, trauma, congenital anomalies, endocrine disorders, tumors, psychiatric disorders, aging, drugs, environmental and industrial pollutants, iatrogenic factors, and miscellaneous diseases. A discussion of current disability compensation guidelines in the United States and Britain is also presented.