Solitary or multiple duodenal diverticula of the primary type are not rare, but diverticulitis is not commonly seen and associated symptoms are unusual. It is rare for this lesion to be the primary target for an abdominal operative procedure. Conflicting reports regarding the incidence of duodenal diverticula and the infrequency of clinically significant duodenal diverticulitis prompted this review of clinical material in an effort to determine the pathological and clinical importance of such a lesion. Material During a 47-year-period (1914-1960 inclusive) one million patients had been examined at a large midwestern clinic,* and of these, 1,064 patients with duodenal diverticula had been so indexed for an incidence of 1.064%. This figure falls into the range of 1% to 6% and an average of 1.73% recorded in the surgical literature for series based upon x-ray diagnosis. A higher incidence, 2% to 22% with an average of 8.6%, is found in autopsy