A 56-year old female presenting with neurological dysfunction is diagnosed with a voluminous cerebral tumour. After complete resection of the lesion, histopathological examination strongly suggests a metastasis of a small cell lung carcinoma. However, extensive work-up showed no evidence for extracerebral primary tumour. Adjuvant treatment was consistent with radiotherapy and cisplatin-based chemotherapy. After five years the patient is doing well without evidence of recurrence. We present the difficult differential diagnosis between a primary brain small cell carcinoma and an occult small cell lung carcinoma. Extrapulmonary small cell cancer (EPSCC) is a distinct clinicopathological entity compared to SCLC, but because of the low incidence, it is often managed in the same way as SCLC. More clinical knowledge based on retrospective analyses and biological insights is required to determine the best therapeutic approach. In any case, it is important to interpret immunohisto-chemical findings with caution in different clinical situations.