The Functional Assessment of Cancer Therapy (FACT)-Kidney Symptom Index (FKSI) was developed and validated to enhance treatment decision-making, practice guidelines, symptom management, and treatment efficacy for kidney cancer patients. Thirty-four symptoms related to the disease were identified and tested. An equal weighting of patient and clinician ratings of the relative importance of each of these items led to production of a 15-item index (FKSI-15) and a 10-item abbreviated option (FKSI-10). To assess psychometric properties, patients completed the FKSI, Functional Assessment of Cancer Therapy-General (FACT-G), Eastern Cooperative Oncology Group-Performance Status Rating (ECOG-PSR), and a Global Rating of Change Scale (GRCS). Patient responses to the FKSI were analyzed for internal consistency, test-retest reliability, convergent and discriminant validity, and responsiveness to change in clinical status. The FKSI-10 showed high internal consistency; correlations between both FKSI-10 and the physical and functional well being domains of the FACT-G were high. The FKSI-10 differentiated patients grouped by ECOG-PSR (all P < 0.001) and discriminated patients based on their GRCS rating. The minimally important difference (MID) range estimate for the FKSI-10 was 2-4 points; the psychometric properties of the FKSI-15 were very similar (MID range, 3-5 points).Thus, the FKSI-15 and FKSI-10 are reliable and valid symptom indices for evaluating kidney cancer patients.