Background Brain metastasis is one of the most important causes of treatment failure in patients with small cell lung cancer (SCLC).This study was conducted to evaluate the effects of prophylactic cranial irradiation (PCI) on survival and brain metastases for patients with limited stage small cell lung cancer in complete remission.Methods Fifty one patients with limited stage SCLC in complete remission after chemoradiotherapy were randomly divided into PCI group (n=26) and control group (n=25).Patients in the PCI group received PCI at a dose of 25.2 to 30.6 Gy in 1.8 to 2.0 Gy per fraction.The Kaplan-Meier method and Log rank test were used to analyse and compare survival rates, and χ2 test was used to compare the incidences of cranial metastases in two groups.Results There was no significant difference in clinical characteristics of patients such as age, sex, effect of treatment before PCI between the two groups.The incidence of brain metastases was 3.8% in the PCI group in contrast to 32.0% in the control group (χ2=5.15, P=0.02).The 1, 3, 5-year survival rates were 84.6%, 42.3%, 34.6% respectively in the PCI group and 72.0%, 32.0%, 24.0% respectively in the control group, with no difference between the two groups (χ2=2.25, P=0.13).No serious sequelae were observed in patients receiving PCI.Conclusion For patients with limited stage SCLC responding completely to chemotherapy plus radiotherapy, PCI can decrease the incidence of brain metastases and improve survival rate.