Background: For patients with a brain metastasis (BM), systemic therapy is usually administered after the completion of radiotherapy, especially in cases of multiple BMs. However, the role of systemic therapy in patients with a limited number of BMs is not clear. Therefore, we conducted a retrospective study to explore this question. Methods: Consecutive patients with a pathologically confirmed malignancy and 1-3 intracranial lesions that had been documented within the last decade were selected from the databases of three hospitals in China. Results: A total of 250 patients were enrolled; of them, 135 received radiotherapy alone and 115 received radiotherapy plus systemic therapy. In patients receiving whole-brain radiation therapy (WBRT) as radiotherapy, 28 received WBRT alone and 35 patients received WBRT plus systemic therapy. Of the patients treated with stereotactic radiosurgery (SRS), 107 received SRS alone and 80 received SRS plus systemic therapy. Multivariate analysis revealed that systemic therapy significantly reduced the risk of mortality compared with radiotherapy alone (hazard ratio [HR] = 0.294, 95% confidence interval [CI] = 0.158-0.548). Further, when the analysis was conducted in subgroups of WBRT (HR = 0.230, 95% CI = 0.081-0.653) or SRS (HR = 0.305, 95% CI = 0.127-0.731), systemic therapy still showed the ability to reduce the risk of mortality in patients with BMs. Conclusion: Systemic therapy after either SRS or WBRT radiotherapy may significantly reduce the risk of mortality of patients with 1-3 BMs.