Background and objective To study the cumulative incidence and surgical treatment of midline incisional hernia (MIH) after cystectomy for bladder cancer. Methods In the nationwide Bladder Cancer Data Base Sweden (BladderBaSe), cystectomy was performed in 5646 individuals. Cumulative incidence MIH and surgery for MIH were investigated in relation to age, gender, comorbidity, previous laparotomy and/or inguinal hernia repair, operative technique, primary/secondary cystectomy, postoperative wound dehiscence, year of surgery, and period-specific mean annual hospital cystectomy volume (PSMAV). Results Three years after cystectomy the cumulative incidence of MIH and surgery for MIH was 8% and 4%, respectively. The cumulative incidence MIH was 12%, 9% and 7% in patients having urinary diversion with continent cutaneous pouch, orthotopic neobladder and ileal conduit. Patients with postoperative wound dehiscence had a higher three-year cumulative incidence MIH (20%) compared to 8% without. The corresponding cumulative incidence surgery for MIH three years after cystectomy was 9%, 6%, and 4% for continent cutaneous, neobladder, and conduit diversion, respectively, and 11% for individuals with postoperative wound dehiscence (vs 4% without). Using multivariable Cox regression, secondary cystectomy (HR 1.3 (1.0-1.7)), continent cutaneous diversion (HR 1.9 (1.1-2.4)), robot-assisted cystectomy (HR 1.8 (1-3.2)), wound dehiscence (HR 3.0 (2.0-4.7)), cystectomy in hospitals with PSMAV 10-25 (HR 1.4 (1.0-1.9)), as well as cystectomy during later years (HRs 2.5-3.1) were all independently associated with increased risk of MIH. Conclusions The cumulative incidence of MIH was 8% three years postoperatively, and increase over time. Avoiding postoperative wound dehiscence after midline closure is important to decrease the risk of MIH.