Non-resectional strategies (NRS) have improved outcomes for a sub-group of patients with perforated diverticulitis. NRS are applicable to patients with non-faeculant peritonitis (Hinchey II and III). Success is dependent on the initial perforation sealing, which Hinchey estimated occurred 'most of the time'. An exact percentage remains ill-defined.We aimed to define the percentage and clinical significance of a persistent perforation in non-faeculant diverticular peritonitis.A retrospective review was conducted of all patients admitted with a diagnosis of perforated diverticulitis between January 1999 and July 2010. Patients undergoing an emergency operation were analysed according to Hinchey and physiological and operative severity scores and compared with histological findings.One hundred fifteen patients were identified. Fifty-three patients underwent a 'resectional' procedure. At surgery, 15 patients had faeculent peritonitis, 27 patients had purulent peritonitis and 11 patients had a contained abscess. Of the patients with non-faeculant peritonitis, 2/9 (22.2 %) Hinchey II and 10/27 (37.1 %) Hinchey III patients had persistent perforation on review of histology. Persistent perforation was associated with a significant increase in morbidity, length of stay, physiological and operative severity score (p = 0.015, 0.011, 0.049 and 0.002, respectively).A proportion of patients with non-faeculant peritonitis have a persistent perforation which is associated with a poorer outcome and is likely to result in failure of a non-resectional management strategy. Updated classification systems and tailored peri-operative investigations are required to identify this sub-group of patients and improve patient outcomes.