Background: Previous studies have pointed to many different prognostic factors for small cell lung cancer (SCLC) but diabetes mellitus (DM) has not been clearly or consistently identified as of prognostic value. The aim of this study was to investigate the prognostic significance of the characteristics of patients and clinical laboratory tests in SCLC. Specifically, we investigated that the impact of DM for survival in the patients receiving first-line etoposide plus cisplatin (EP) chemotherapy. Methods: We retrospectively reviewed 161 patients with SCLC with a focus on DM and other potential prognostic variables were chosen for univariate and multivariate analyses with respect to survival. Result: Among the sixteen variables of univariate analysis, five were identified to have prognostic significance: performance status (PS) (p<0.001), stage (p=0.001), DM (p=0.005), serum albumin (p<0.001) and hemoglobin levels (p=0.03). Multivariate analysis showed PS, stage and serum albumin level to be independent prognostic factors for survival (p=0.02, p=0.02 and p=0.009 respectively), but DM was not an independnet factor. Conclusion: In conclusion, PS, stage and serum albumin level were identified as important prognostic factors, while DM at the time of diagnosis of SCLC did not have prognostic importance for survival.