The prevalence of Campylobacter pylori (CP) in gastric biopsies from cancer patients has not been previously studied. We reviewed 112 gastric biopsies from 78 adult patients at a cancer hospital. The patients had a previous history or current diagnosis of gastric or esophageal carcinoma (26 patients), gastric lymphoma (15 patients), gastric stromal tumor (three patients), carcinoid tumor (two patients), nongastroesophageal malignancy (29 patients), or atrophic gastritis with nonhealing ulcer (three patients). The biopsies were stained with hematoxylin-eosin (H&E), Warthin-Starry, Giemsa, and Brown-Hopps. CP was identified in 30 biopsies from 26 patients. Eighteen of the biopsies showed active gastritis, nine showed chronic inflammation/intestinal metaplasia, and one contained an ulcer. CP was also identified in two stomachs bearing tumors (one adenocarcinoma, one carcinoid tumor). Active gastritis was present without CP in nine biopsies, including three from patients on chemotherapy and one from a patient with bile reflux. The organism was detected by the Warthin-Starry stain in 30 biopsies. The Giemsa stain was positive in 27, Brown-Hopps in 27, and H&E in 24. Non-CP bacteria were identified in the Brown-Hopps in seven cases and were mistaken for CP in H&E stains in two. We conclude that CP is frequently found in the cancer patient with active gastritis and is an occasional finding in tumor-bearing stomachs. Special stains are useful in identifying CP, and the Brown-Hopps is helpful in distinguishing CP from other bacteria.