PURPOSE: The Patient-Reported Outcome Measurement Information System Cognitive Function Short Form 8a  (PROMIS Cog) could provide a shorter, useful alternative to the often used Functional Assessment of Cancer Therapy - Cognition (FACT-Cog) in research and clinical care. This study aimed to determine the convergent validity and internal reliability of the PROMIS Cog in 3 separate samples of breast cancer survivors and to explore clinical cut points. METHODS: Data from three samples of breast cancer survivors were used for this secondary analysis. Convergent validity was determined by evaluating correlation strength among the derived PROMIS Cog and measures of depression, anxiety, stress, fatigue, sleep, loneliness, the FACT-Cog . Clinical cut-points for the PROMIS Cog were determined by plotting the receiver operating characteristic curves. RESULTS: 3 samples of breast cancer survivors (N = 471, N = 132, N = 90) were included. Absolute values of correlations demonstrating convergent validity ranged from 0.21 to 0.82, ps < 0.001, and were comparable to correlations with the full FACT-Cog 18 item perceived cognitive impairments (PCI) scale. ROC curve plots indicated a clinical cut off < 34 for the combined sample. CONCLUSION: The 8-item PROMIS Cog demonstrated good convergent validity and internal reliability in breast cancer survivors, comparable to the 18-item FACT-Cog PCI. The PROMIS Cog 8a is a brief self-report measure that can be easily incorporated into cancer-related cognitive impairment research designs or used in clinical settings.