Tumor cells circulate in the blood, but it is unusual to find cancer cells on a routine peripheral smear. The term carcinocythemia is used to describe this phenomenon. Four patients have been reported previously with small cell lung cancer and carcinocythemia. A fifth case is described in this article. These patients presented with advanced disease and had generalized lymphadenopathy and liver involvement; 3 had splenic metastases. All of these patients experienced rapid clinical deterioration. Death occurred 3 days to 2 weeks from the time carcinocythemia was detected. The presence of small cell carcinocythemia can be one of the manifestations of end-stage disease and is associated with an extremely poor prognosis.