Studies examining long-term outcomes following resolution of an acute diverticular abscess have been limited to single-institution chart reviews. This observational cohort study compared outcomes between elective colectomy and non-operative management following admission for an initial acute diverticular abscess.The Statewide Planning and Research Cooperative System was queried for unscheduled admissions for an initial acute diverticular abscess in 2002-2010. Bivariable and propensity-matched multivariable analyses compared stoma rates and use of healthcare in patients who had an elective resection and those receiving non-operative management. Diverticulitis recurrence rates were analysed for non-operative management.Among 10 342 patients with an initial acute diverticular abscess, one-third (3270) underwent surgical intervention within 30 days despite initial non-operative management. Of the remaining 7072 patients, 1660 had an elective colectomy within 6 months. Of 5412 patients receiving non-operative management, 1340 (24·8 per cent) had recurrence of diverticulitis within 5 years (median 278 (i.q.r. 93·5-707) days to recurrence). Elective colectomy was associated with higher stoma rates (10·0 per cent, compared with 5·7 per cent for non-operative observation, P < 0·001; odds ratio 1·88, 95 per cent c.i. 1·50 to 2·36), as well as more inpatient hospital days for diverticulitis-related admissions (mean 8·0 versus 4·6 days respectively, P < 0·001; incidence rate ratio (IRR) 2·16, 95 per cent c.i. 1·89 to 2·47) and higher mean diverticulitis-related cost (€70 107 versus €24 490, P < 0·001; IRR 3·11, 2·42 to 4·01).Observation without elective colectomy following resolution of an initial diverticular abscess is a reasonable option with lower healthcare costs than operation.