Purpose: The study aimed to investigate long-term mortality, recurrence, and death related to recurrence for patients admitted with acute diverticulitis with abscess formation (Hinchey stage Ib-II). Methods: The cohort was identified by linking administrative registers for all Danish citizens in years 2000–2012. Patients were identified from ICD-10 discharge codes and stratified according to treatment (antibiotics, percutaneous abscess drainage, or surgery). Results: From 6,641,672 persons, 3148 patients were identified with acute diverticulitis with abscess formation. Survival was comparable between treatment groups with a 1-year survival of 81–83% and a 5-year survival of 66–67% (p = 0.66). Glucocorticoid usage prior to admission increased risk of mortality with hazard ratio 1.64 (95%CI 1.39–1.93), 1.77 (1.20–2.63), and 1.92 (1.07–3.44) for the antibiotics, drainage, and operative treatment group, respectively. Drainage treatment increased risk of recurrence with sub-distribution hazard (SDH) of 1.52 (1.19–1.95) and operative treatment decreased risk with a SDH of 0.55 (0.32–0.93), both compared with antibiotic treatment (p = 0.0001). Recurrence occurred in 23.6% (18.5–30.1%) of patients in the drainage group, 15.5% (13.9–17.3%) in the antibiotics group, and 9.1% (5.1–16.1%) in the operative group. Recurrence-related mortality was 2.0% (0.9–4.4%) for the drainage group, 1.1% (0.7–1.8%) for the antibiotics group, and 0.6% (0.1–4.3%) for the operative group (p = 0.24). Most recurrences and recurrence-related mortality occurred within the first year after primary admission. Conclusions: This study with complete national data revealed a high mortality and recurrence rate after diverticular abscesses. Survival was comparable between treatment groups, but patients treated with drainage had significantly higher risk of recurrence.