This study was undertaken to assess the appropriate management of patients with diverticulitis complicated by fistula formation. A retrospective chart review was conducted on patients with symptoms of a fistula who presented between 1975 to 1995. There were 42 patients (32 women, 76%; 10 men, 24%) who ranged in age from 46 to 89 years (mean 69.8 +/- 9.8). Six patients had multiple fistulas. The types of fistulas included colovesical (48%), colovaginal (44%), colocutaneous (4%), colotubal (2%), and coloenteric (2%). Operative procedures consisted of resection and primary anastomosis in 38 patients and a Hartmann's operation in one. Three patients were managed conservatively with antibiotics (two due to poor performance status, the third due to resolution of symptoms). There were no operative deaths. The postoperative course was uncomplicated in 69%, while 12 patients (31%) experienced 19 complications (40%). These consisted of urinary tract infection (9.5%), atelectasis (7.1%), prolonged ileus (4.8%), arrhythmias (4.8%) and renal failure, myocardial infarction, pseudomembranous colitis, peroneal nerve palsy, unexplained fever, pulmonary edema (2.4% each). There were no anastomotic leaks and no deaths. Hospital stay ranged from 6 to 31 days (mean 12.3 +/- 7.6). Fistulas due to diverticulitis were safely managed by resection and primary anastomosis without mortality and with acceptable morbidity in this series. Patients deemed to be poor operative risks can be managed with a course of nonoperative treatment.