Aims: To explore factors that may predispose patients to reoperation after sacral neuromodulation (SNM). Methods: Patients enrolled in our longitudinal neuromodulation database were reviewed. Medical records data, and voiding diaries, Interstitial Cystitis Symptom-Problem Indices (ICSI-PI), and Overactive Bladder Questionnaires (OAB-q) at baseline and 3 months were analyzed with Pearson's chi(2), Fisher's Exact test, Wilcoxon rank tests, and multivariable logistic regression. Results: Of 407 patients, 134 (33%) had at least one reoperation over median 28.9 months follow-up (range 1.6-121.7); 78/407 (19%) were revised, and 56/407 (14%) were explanted. The most common reason for reoperation was lack of efficacy/worsening symptoms (n = 87). The reoperations group had a higher proportion of women(P = 0.049), lower mean body mass index (BMI; P = 0.010), more reprogramming events (P<0.0001), longer median follow-up (P = 0.0008), and higher proportions with interstitial cystitis (P = 0.013), using hormone replacement therapy (P = 0.0004), and complications (P<0.0001). Both reoperations/no reoperations groups had similar improvements in ICSI-PI (P<0.0001 for both), OAB-q severity (P<0.0001 for both) and quality of life (P<0.0001 for both). On multivariate analysis, only longer follow-up (P = 0.0011; OR 1.048; CI 1.019, 1.078) and having a complication (P<0.0001; OR 23.2; CI 11.47, 46.75) were significant predictors of reoperations. In women only, using HRT at time of implant was also predictive of reoperation (P = 0.0027; OR 3.09; CI 1.48, 6.46). Conclusions: In this largest known series to date, one third of the patients required reoperation and the most common reason was lack of efficacy/ worsening symptoms. Ongoing study is needed as the technology continues to evolve. (C) 2015 Wiley Periodicals, Inc.