In 2,861 consecutive patients undergoing appendicectomy for clinically suspected appendicitis an enteric pathogen was isolated from the appendix in almost 7% using an optimal combination of culture media. The pathogenic Yersinia enterocolitica serotypes 03 and 09 predominated (3.6%), followed by Campylobacter and nontyphoid Salmonella. The same pathogen was isolated from the stool in 72.5% of patients with a culture-positive appendix and in 84.1% of those positive for a pathogenic Yersinia. Conversely, no pathogenic Yersinia were isolated in 326 gynaecologic control patients, in whom a normal appendix was removed. No frank appendicitis but mesenteric adenitis and/or terminal ileitis were found in 62.3% of 138 patients with a culture positive appendix, and in 74.6% of those positive for a pathogenic Yersinia. Histologic findings available in 135 patients showed acute suppurative appendicitis in only six (4.5%) patients, and in only one of 73 (1.4%) positive for a pathogenic Yersinia. In contrast, 46.8% of a group of 345 culture-negative appendices showed acute inflammation. A positive stool culture in a patient with suspected appendicitis, if consistent with sonographic and clinical findings, should be taken as strong evidence against the presence of true appendicitis.