A 62-yr-old man was referred for management of GI polyposis. Large bowel polyps were initially diagnosed >25 yr ago, and the patient had undergone multiple colonoscopies and polypectomies. Personal and family history were notable for thyroid goiter and hypothyroidism. Physical examination was notable for lingular papillomatosis. No cutaneous lesions were seen. Upper endoscopy revealed esophageal glycogen acanthosis. There were multiple polyps throughout the stomach and the small and large intestines. Histology of these polyps showed multiple cell types including juvenile polyps, inflammatory polyps with fibromuscular proliferation and lamina propria ganglion cells, and focal adenomatous change. A clinical diagnosis of Cowden syndrome was made. Mutation analysis revealed a variant in exon 8 of the PTEN gene. Direct sequencing revealed a germline heterozygous C.892-895InsA, which is predicted to result in a truncated PTEN protein. Cowden syndrome is an underdiagnosed, underrecognized, autosomal dominant, inherited syndrome. For the gastroenterologist, esophageal acanthosis and multiple hamartomatous polyps should suggest the diagnosis. Sensitive molecular diagnostic tests looking for mutations in the appropriate genes are clinically available. Together with genetic counseling, molecular diagnostic testing will allow more accurate risk assessment and surveillance for cancer for both the patient and family members.