Abstract Background Outpatient treatment of uncomplicated acute diverticulitis is safe and effective. The aim of this study was to determine the impact of outpatient treatment on the reduction of healthcare costs. Patients and methods A retrospective cohort study comparing two groups was performed. In the outpatient treatment group, patients diagnosed with uncomplicated acute diverticulitis were treated with oral antibiotics at home. In the hospital treatment group, patients met the criteria for outpatient treatment but were admitted to hospital and received intravenous antibiotic therapy. Cost estimates have been made using the hospital cost accounting system based on total costs, the sum of all variable costs (direct costs) plus overhead expenses divided by activity (indirect costs). Results A total of 136 patients were included, 90 in the outpatient treatment group and 46 in the hospital group. There were no differences in the characteristics of the patients in both groups. There were also no differences in the treatment failure rate in both groups (5.5% vs 4.3%; p =0.7). The total cost per episode was significantly lower in the outpatient treatment group (882±462 vs 2376±830 euros; p =0.0001). Conclusions Outpatient treatment of acute diverticulitis is not only safe and effective but also reduces healthcare costs by more than 60%.