Incisional hernias are a frequent complication following robotic radical prostatectomy. Observational data in men undergoing robotic prostatectomy suggest that transverse closure resulted in lower hernia rates than vertical closure. We sought to compare the incidence of incisional hernia after robotic radical prostatectomy after vertical and transverse extraction site closure. We conducted a clinically integrated, crossover, cluster randomized trial at a single tertiary referral center (January 2016-September 2021) comparing the rate of hernia after transverse vs vertical extraction site excision in 1356 patients treated with minimally invasive radical prostatectomy. The primary outcome was between-group incidence of incisional hernia within 15 months of prostatectomy defined by physical examination and self-reported patient surveys. Overall, 197 (20%) patients developed an incisional hernia within 15 months, 797 did not have an incisional hernia within this period, and 362 had missing outcome data regarding incisional hernia. We found no significant difference in hernia rates between the 2 incision types (absolute between-group difference 1.8%; 95% CI -3.4%, 6.6%; P = .5) in the primary analysis or in the 3 sensitivity analyses. Notably, because of the inclusive definition of hernia used, these data cannot be used as an estimate of the true prevalence of incisional hernia. Surgeons should choose the incision and closure approach they are most comfortable with when extracting specimens. Studies of modifications to the surgical technique are best conducted as randomized comparisons, and the clinically integrated, crossover, cluster randomized trial allows large trials to be completed at a single center and at low cost. ClinicalTrials.gov: NCT01407263.