Olfactory hallucinations, known as phantosmias, are a poorly understood phenomenon. It has been associated with a wide rage of differential diagnosis. However, most cases are idiopathic. The author's presents a 70-year-old man with olfactory hallucinations as the predominant symptom of the brain metastatic small cell carcinoma in order to clarify the causal relationship. Little is known about the origin and clinical significance of phantosmias. It can even be the predominant symptom of an underlying small cell metastatic brain tumor as presented in our case. Therefore a detailed history of the symptoms along with a neurological and physical examination and routine laboratory and screening tests should be provided in order to exclude any organic causes.