Small cell lung cancer is the most aggressive lung cancer subtype. The standard treatment approach is based on cisplatin regimens. Although response rates to treatment are approximately 60-80%, the median survival is still very poor. Excision repair cross complementation group 1 (ERCC1) is an enzyme that removes cisplatin-induced DNA adducts and has been related with prognosis and cisplatin response. Topotecan is the standard treatment as second-line therapy and it is an inhibitor of topoisomerase I (TOP I). We selected 76 patients with small cell lung (SCLC) to analyze the ERCC1 and TOP I mRNA expression. ERCC1 was studied both by quantitative PCR and immunohistochemistry. A significant association was found between the inmunohistochemistry expression of ERCC1 and the lack of platinum response (p=0.001). Moreover, low levels of TOP I RNA were shown to be linked to cisplatin response (p=0.002). In the survival analysis, a significant correlation between a better PFS with a low TOP I RNA expression as well as a negative ERCC1 inmunostaining were found, in both cases with a significant p-value (p=0.02 and 0.009, respectively). In summary, our results suggest the use of ERCC1 immunohistochemistry and TOP I mRNA analysis to predict cisplatin response and prognosis in SCLC patients.