There has been increasing application of endoscopic ablation therapy for patients with high-grade dysplasia (HGD) and Barrett's esophagus (BE). Three cases are reported in which the patient developed adenocarcinoma of the gastric cardia after thermal ablation of HGD. A definition of BE including endoscopic abnormality and intestinal metaplasia by biopsy was used. Strict and standardized criteria were utilized for the endoscopic landmarks. Three cases are reported with long-segment BE and a nodule or mass in the endoscopic cardia post-thermal ablation. Biopsies documented adenocarcinoma of the gastric cardia. The development of adenocarcinoma of the cardia is unexpected. Speculation is offered as to the potential of increased proliferation and mutations at the new squamocolumnar interface after endoscopic ablation therapy to explain this association.