This study aimed to evaluate the imaging findings and prognostic factors after whole-brain radiotherapy in patients with carcinomatous meningitis from breast cancer.A retrospective analysis of imaging data and prognostic factors was performed in patients treated with whole-brain radiotherapy or whole-brain/spine radiotherapy immediately after the first diagnosis of carcinomatous meningitis from breast cancer at our hospital from January 1, 2010 to December 31, 2018. Statistical significance was set at P < .05 (two-tailed).All patients (n = 31) were females with the mean age of 58.0 ± 11.0 years. The breast cancer subtypes were luminal (n = 14, 45.1%), human epidermal growth factor receptor 2 (HER2)-positive (n = 9, 29.0%), and triple-negative (n = 8, 26.0%) breast cancer. Brain metastasis and abnormal contrast enhancement in the sulci were observed in 21 (67.7%) and 24 (80.6%) patients, respectively. The median survival time after cancerous meningitis diagnosis was 62 (range, 6-657) days. Log-rank test showed significant differences in median survival time after cancerous meningitis diagnosis: 18.0 days for subjects treated with 30 Gy in < 10 fractions (n = 7) vs 78.5 days for subjects treated with 30 Gy in ≥10 fractions (n = 24) (P < .01) and 23.0 days for the triple-negative subtype vs 78.5 days for the other subtype (P < .01) groups. Univariate analysis using the Cox regression model showed significant differences in median survival time after cancerous meningitis diagnosis between the group treated with 30 Gy in <10 fractions and the group treated in ≥10 fractions (hazard ratio [HR] 0.08, 95% confidence interval [CI], 0.03-0.26; P < .01), and between the triple-negative subtype and the other subtypes (HR = 5.48; 95% CI, 1.88-16.0; P < .01) groups.Discontinuation of whole-brain radiotherapy and the presence of triple-negative breast cancer were indicators of poor prognosis.