Purpose: In order to personalize multimodal treatment regimens in limited-stage small cell lung cancer (LS-SCLC), a survival score for these patients was proposed. The aim of this study is to validate the score in an independent external patient cohort. Methods: We collected data of 78 patients treated with chemoradiotherapy for LS-SCLC between 2004 and 2015. The survival score was calculated by independent prognostic factors: gender, Karnofsky performance status, tumor substage, and hemoglobin level before treatment. Scoring points were derived from 2-year survival rates divided by 10 and the values for each prognostic factor were tallied. Three risk subgroups were defined (high, intermediate, low risk: 9–13, 14–18, 19–26 points). The 2-year survival rate of each subgroup from the original study was compared to its corresponding subgroup from the validation cohort. Results: Median survival time in the entire validation cohort was 17 months (range: 1–123 months). The 2-year survival rates were 0% in the 9–13, 35% in the 14–18, and 43% in the 19–26 points group, respectively (p = 0.018). The difference in 2-year survival between the 9–13 points and the 14–18 points group was significant in the validation cohort (p = 0.007) as well after stratification of concurrent chemoradiotherapy (p < 0.001), whereas the difference between the 14 and 18 points and the 19–26 points group was not significant (p = 0.602, p = 0.770). Conclusion: The score was reproducible to estimate the 2-year survival rate of patients with LS-SCLC, especially in the high- and intermediate-risk subgroups. In order to improve the differentiation between patients with an intermediate and favorable survival prognosis, the scoring system needs further development.