In extensive disease of small cell lung cancer a doubling of the one-year-survival rate was reported in August 2007 by prophylactic cranial irradiation applied to patients who experienced any response to initial chemotherapy. We discuss the treatment concept of extensive disease in the face of the latest results and older studies with additional thoracic irradiation in this subgroup. A randomized trial with prophylactic cranial irradiation published in 1999 demonstrated an improvement of 5-year-overall-survival for complete responders (at least at distant levels) receiving additional thoracic radiochemotherapy compared to chemotherapy alone (9.1% vs. 3.7%). But, these results were almost neglected and thoracic radiotherapy was not further investigated for good responders of extensive disease. However, in the light of current advances by prophylactic cranial irradiation these findings are noteworthy on all accounts. Considering both, a possible interpretation of these data could be a survival benefit of local control by simultaneous thoracic radiochemotherapy in the case of improved distant control due to chemotherapy and prophylactic cranial irradiation. Furthermore the question arises whether the tumor biology indicated by the response to chemotherapy should be integrated in the present classification.