Background: The Distress Thermometer (DT) is widely recommended for screening for distress after cancer. However, the validity of the DT in men with prostate cancer and over differing time points from diagnosis has not been well examined. Method: Receiver operating characteristics analyses were used to evaluate the diagnostic accuracy of the DT compared with three commonly used standardised scales in two prospective and one crosssectional survey of men with prostate cancer (n = 740, 189 and 463, respectively). Comparison scales included the Impact of Event Scale - Revised (IES-R, Study 1), the Hospital Anxiety and Depression Scale (HADS, Study 2) and the Brief Symptom Inventory-18 (BSI-18, Study 3). Results: Study 1: the DT showed good accuracy against the IES-R at all time points (area under curves (AUCs) ranging from 0.84 to 0.88) and sensitivity was high (>85%). Study 2: the DT performed well against both the anxiety and depression subscales for HADS at baseline (AUC = 0.84 and 0.82, respectively), but sensitivity decreased substantially after 12 months. Study 3: validity was high for the anxiety (AUC = 0.90, sensitivity = 90%) and depression (AUC = 0.85, sensitivity = 74%) subscales of the BSI-18 but was poorer for somatization (AUC = 0.67, sensitivity = 52%). A DT cutoff between =3 and =6 maximised sensitivity and specificity across analyses. Conclusions: The DT is a valid tool to detect cancer-specific distress, anxiety and depression among prostate cancer patients, particularly close to diagnosis. A cut-off of =4 may be optimal soon after diagnosis, and for longer-term assessments, =3 was supported.