OBJECTIVES: The Functional Assessment of Cancer Therapy – Kidney Symptom Index (FKSI) is a 15-item scale that was developed and validated to assess symptoms and concerns of advanced kidney cancer patients. The aim of this study was to evaluate the factor structure of FKSI for possibly useful sub-scales and assess the reliability of the sub-scales. METHODS: Data for this study were obtained from a phase III clinical trial of 903 advanced renal cancer patients. Patients were administered FKSI questionnaire at baseline. Baseline data were analyzed using exploratory factor analysis with oblique rotation (promax) to evaluate the dimensional structure of FKSI. The internal consistency of the subscales and overall scale was assessed using Cronbach's alpha. RESULTS: Four factors were identified consisting of 13 of the 15 items of FKSI. The first factor had two items related to pain symptoms; the second factor had two items related to respiratory symptoms; the third factor had five items related to general symptoms of the disease and; the fourth factor had four items related to quality of life. All four factors had good reliability (alphas > 0.70). The internal consistency of the overall 13-item scale was excellent (alpha = 0.83). CONCLUSION: A four-factor solution consisting of 13 items could easily be labeled with clinically-meaningful concepts, indicating the possibility of four underlying dimensions of kidney cancer symptomatology: pain, respiratory, general symptoms and quality of life. Findings supported the internal consistency of four sub-scales and overall 13-item scale. Sub-scale scores and the total index are reliable and valid measure that can be used to determine the effect of drug therapies on specific symptoms and concerns of advanced kidney cancer.