Although dizziness is a common symptom in both primary care and referral practices, the relative frequency of various causes has not been well delineated. A MEDLINE search identified 12 articles containing original data on the etiology of dizziness in consecutive patients. Study sites included primary care offices (n = 2), emergency room (n = 4), and referral clinics (n = 6). Each study's strength of design was graded using nine quality criteria. Dizziness was attributed to a peripheral vestibulopathy in 44% of patients, a central vestibulopathy in 11%, psychiatric causes in 16%, other conditions in 26%, and an unknown cause in 13%. Certain serious causes were relatively uncommon, including cerebrovascular disease (6%), cardiac arrhythmia (1.5%), and brain tumor (<1%). Dizziness is due to vestibular or psychiatric causes in more than 70% of cases. Since serious treatable causes appear uncommon, diagnostic testing can probably be reserved for a small subset of patients.