Olfactory hallucinations have been reported in association with numerous neurologic and psychiatric disorders. We present four cases of olfactory hallucinations accompanying migraine headache. Each patient had a normal neurologic examination, normal cranial CT, and normal EEG. All patients experienced relief of olfactory hallucinations and headaches with propranolol therapy. The specific subjective features of olfactory hallucinations associated with various neurologic and psychiatric disorders are reviewed, and a classification of these sensory phenomena along well-defined axes is presented. Olfactory hallucinations associated with migraine are usually perceived as extrinsic, real and unpleasant, features which are also common in such hallucinations associated with other neurologic diseases. Psychiatric olfactory hallucinations are most often perceived as intrinsic, unreal, or both. These subjective aspects of the hallucinations are helpful in differential diagnosis, but careful evaluation is necessary to exclude other neurologic disorders.