BACKGROUND & AIMS Fundic gland polyps (FGPs) are common in familial adenomatous polyposis (FAP) but have been considered nonneoplastic. Gastric carcinoma arises from FGPs in FAP presumably from a dysplasia-carcinoma pathway. Our study examined the prevalence of FGPs and FGP dysplasia in FAP and identified endoscopic or demographic features associated with FGPs and dysplasia. METHODS Demographic and endoscopic information were obtained prospectively from 75 consecutive subjects undergoing upper-endoscopic surveillance for FAP. Systematic biopsy specimens of FGPs, normal-appearing fundic mucosa, and antral mucosa for Helicobacter pylori were obtained. Multivariable analysis assessed the association of demographic or endoscopic factors with the presence of FGP or FGP dysplasia. RESULTS FGPs were detected in 88% of subjects and were dysplastic in 41% (38% low grade, 3% high grade). H pylori infection was rare in subjects with vs without FGPs (1.5% vs 33.3%, P = .005). In the multivariable analysis larger FGP size (odds ratio [OR], 4.0; 95% confidence interval [CI], 1.1-14.4), higher stage of duodenal polyposis (OR, 2.3; 95% CI, 1.2-4.5), and antral gastritis (OR, 11.2; 95% CI, 1.2-103.9) were associated with FGP dysplasia. Exposure to acid-suppressive medications was associated with a marked decrease in dysplastic FGPs (OR, 0.14; 95% CI, 0.03-0.64). CONCLUSIONS The majority of FAP patients have FGPs and nearly half will have dysplastic FGPs. There is an inverse relationship between H pylori and FGPs. FGP dysplasia is associated with larger polyp size, increased severity of duodenal polyposis, and antral gastritis. Acid-suppressive therapy use appears protective against dysplasia in FGPs.