Fear of cancer recurrence (FCR) is one of the major existential unmet needs of cancer survivors. Due to growing availability of evidenced-based interventions for high FCR, valid and reliable brief measures of FCR are needed. This study aimed to validate the 6-item Cancer Worry Scale (CWS) and to establish a cut-off score for high FCR.Participants in this study were 1033 cancer survivors and patients recruited as part of 5 existing studies on FCR involving patients and survivors with gastro-intestinal stromal tumors, colorectal, breast, and prostate cancer. De-identified data of the CWS, Fear of Cancer Recurrence Inventory (FCRI), Impact of Event Scale, Hospital Anxiety and Depression Scale, and EORTC-QLQ-C30 were amalgamated for the analyses. Confirmatory factor analysis of the CWS was performed. Sensitivity and specificity were tested with the FCRI as gold standard.Results confirmed that the 6-item version of the CWS maintained good construct validity, convergent and divergent validity, and high internal consistency (α 0.90). The optimal cut-off for the 6-item CWS was 9 versus 10 using the 12 vs 13 FCRI-SF score (sensitivity 82%, specificity 83%) and the 15 vs 16 FCRI-SF score (sensitivity 88%, specificity 73%). Using the highest FCRI-SF cut-off (21 vs 22), the optimal CWS cut-off was 11 vs 12 (sensitivity 88%, specificity 81%).The present results provide researchers and clinicians with a brief valid and reliable measure of FCR which is suitable for measuring FCR in cancer patients and survivors.