OBJECTIVE This study aimed to assess the association between the Distress Thermometer (DT) score and risk of suicide in patients with cancer. In addition, we aimed to determine the best cutoff score to predict patients at risk of suicide. METHODS From 2015 to 2016, we retrospectively collected data on patients with cancer. DT scores were collected, and the association between DT score and risk of suicide (suicide ideation or death ideation) was analyzed. Furthermore, receiver operating characteristic (ROC) analysis was performed to identify the appropriate cutoff score for predicting risk of suicide. RESULTS A total of 260 patients with cancer were included, and suicidal ideation was identified in 33 cases referred for psychological intervention. The DT scores of the patients with suicidal ideation were significantly higher than those of patients without suicidal ideation (6.30±2.11 vs. 4.29±1.72, p<0.05). In addition, the area under the ROC curve for predicting risk for suicide was 0.758. The cutoff DT score of 3 had the highest sensitivity of 1.00 to rule out suicidal ideation, while 9 had the highest specificity of 1.00 to rule in suicidal ideation. Moreover, the appropriate cutoff DT score to predict patients with suicidal ideation was 5, with a sensitivity of 0.52, specificity of .84, positive likelihood ratio of 3.24, and negative likelihood ratio of 0.58. CONCLUSIONS The DT score may be a helpful clinical tool to evaluate emotional distress and risk of suicide in patients with cancer. Clinically, for DT scores greater than 5 in patients with cancer, the risk of suicide greatly increases. In view of the DT's widespread use internationally by non-mental health clinicians in cancer to guide the need for specialist mental health interventions, its potential utility in also predicting suicide risk is of great interest.