Simple SummaryRobot-assisted prostatectomy is one of the main therapeutic options for localized prostate cancer. Lymphoceles are one of the major causes of complications after robot-assisted radical prostatectomy and pelvic lymph node dissection. Because the data on risk factors for lymphoceles remains unclear and inconclusive, they were investigated in the present study using the data set of the prospective randomized trial ProLy. In this study, high BMI was found to be an independent predictor for the occurrence of lymphoceles and symptomatic lymphoceles. In addition, a longer surgical time proved to be another risk factor for the postoperative occurrence of lymphoceles.AbstractLymphoceles (LC) occur in up to 60% after robot-assisted radical prostatectomy (RARP) and pelvic lymphadenectomy (PLND). In 2–10%, they are symptomatic and may cause complications and require treatment. Data on risk factors for the formation of lymphoceles after RARP and PNLD remain sparse in the urologic literature and are inconclusive to date. The underlying data of this secondary analysis were obtained from the prospective multi-center RCT ProLy. We performed a multivariate analysis to focus on the potential risk factors that may influence lymphocele formation. Patients with LC had a statistically significant higher BMI (27.8 vs. 26.3 kg/m2,p< 0.001; BMI ≥ 30 kg/m2: 31 vs. 17%,p= 0.002) and their surgical time was longer (180 vs. 160 min,p= 0.001) In multivariate analysis, the study group (control vs. peritoneal flap,p= 0.003), BMI (metric,p= 0.028), and surgical time (continuous,p= 0.007) were independent predictors. Patients with symptomatic lymphocele presented with higher BMI (29 vs. 26.6 kg/m2,p= 0.007; BMI ≥ 30 kg/m2: 39 vs. 20%,p= 0.023) and experienced higher intraoperative blood loss (200 vs. 150 mL,p= 0.032). In multivariate analysis, BMI ≥ 30 kg/m2vs. < 30 kg/m2was an independent predictor for the formation of a symptomatic lymphocele (p= 0.02). High BMI and prolonged surgical time are general risk factors for the development of LC. Patients with a BMI ≥ 30 kg/m2had a higher risk for symptomatic lymphoceles.