Background: Much research has confirmed the favorable effect of irinotecan/cisplatin (IP) and etoposide/cisplatin (EP) on extensive-stage small cell lung cancer (E-SCLC). This study investigated two sequential orders of IP and EP in the treatment of E-SCLC. We also compared the efficacy and safety of IP and EP in first-line chemotherapy in E-SCLC. Methods: Ninety-three untreated patients with E-SCLC were randomly allocated to two groups. Group A received IP as first-line therapy until progression and then changed to EP; group B received EP as first-line therapy until tumor progression followed by IP. The primary endpoints were overall survival and time to second tumor progression. The secondary endpoints were first progression-free survival (PFS), ie, time from randomization to first occurrence of tumor progression after first-line treatment with IP or EP, tumor response, and safety of the different sequential treatment orders of IP and EP. Results: Median overall survival was 15.4 months in group A (IP followed by EP) versus 15.7 months in group B (EP followed by IP; P=0.483). The median time to second tumor progression was 9.5 months in group A versus 9.9 months in group B (P=0.361). As first-line and second-line therapy, IP achieved a 95.9% and 60% disease control rate, respectively, and EP achieved 95.6% and 59% disease control rate. The median first PFS was not significantly different between group A and group B (6.5 months and 6.3 months, respectively; P=0.256). Grade 3/4 diarrhea appeared to be significantly more frequent with IP than with EP. The probability of anemia and thrombocytopenia was not significantly different between the two groups. However, significantly more patients who received the IP regimen as second-line treatment developed grade 3/4 neutropenia than those who received the IP regimen as first-line therapy. Conclusion: There were no statistically significant differences in between the two sequences of IP and EP in the treatment of E-SCLC. Except EP regimen, IP may be another reserved regimen in the first-line treatment of E-SCLC.