We analyzed telomere length and telomerase activity in intestinal metaplasia (IM), adenoma, and cancer of the stomach and studied the stages at which the cells acquire telomerase activity in carcinogenesis and also the correlation between telomerase activity and telomere length. Telomerase activity was detected in 15%, 45%, 89% of IM, adenomas, and cancers. Telomere lengths shortened as normal mucosa changed into IM and more into adenoma. Gastric cancers showed a broad range of telomeric length. The shortest telomere length was found among gastric adenomas. These results suggest that telomerase is expressed during early phase of gastric carcinogenesis but the activity at that stage is not strong enough to fully restore the reduced telomeric DNA.