To determine the effect of frailty on patient outcomes including any complication, Clavien-Dindo IV (CDIV) (intensive care unit-level) complications, and 30-day mortality for robotic-assisted radical prostatectomies (RARP) patients in comparison to other predictive indices using the modified frailty index (mFI).Patients undergoing RARP from 2008 to 2014 for a prostate cancer-related diagnosis were queried using the American College of Surgeons National Surgical Quality Improvement Program (ACS-NSQIP) database. The mFI was developed using the Canadian Study of Health and Aging Frailty Index as a model. The mFI was compared with other associative indices such as the American Society of Anesthesiology (ASA) classification and the Charlson comorbidity index (CCI). Rates of CDIV complications and 30-day mortality were analyzed based on mFI score using SAS version 9.22.A total of 23,104 patients undergoing RARP were queried. RARP patients with the highest frailty score (≥3) had an adjusted odds for CDIV complications of Odds ratio of 12.107 (CI: 2.800-52.351, P< 0.005) in comparison with nonfrail RARP patients. These odds were higher than the ASA and Charlson comorbidity index. Additionally, a variable combining mFI and ASA had fair sensitivity and specificity for predicting 30-day mortality in RARP patients (C-statistic = 0.7097, P<0.0001).Increasing mFI scores are associated with worsening outcomes for patients undergoing RARP. A combined mFI and ASA variable can be used to predict 30-day mortality for RARP patients better than mFI or ASA alone.