AIM:To validate the total illness burden index for prostate cancer (TIBI-CaP) in castration-resistant prostate cancer (CRPC) patients. PATIENTS & METHODS:Baseline comorbidity scores collected using the TIBI-CaP were compared with the baseline patient-reported health-related quality of life using the SF-12v2 and FACT-P questionnaires in 302 patients enrolled in the Treatment Registry for Outcomes in CRPC Patients (TRUMPET). RESULTS:Baseline TIBI-CaP scores were negatively correlated with all baseline SF-12v2 domain/composite (p < 0.001) and FACT-P subscale/total (p < 0.020) scores. There was a significant decreasing linear trend in SF12v2 and FACT-P scores over the categories based on TIBI-CaP quartiles of comorbidity burden (from 'least' to 'severe'). CONCLUSION:The TIBI-CaP is a valid measure of comorbidity burden in patients with CRPC in the real world.