The reliability of endoscopic ultrasonography (EUS) in follow-up management of gastric lymphomas has not been clearly validated. We conducted a retrospective analysis on 23 patients, 12 affected by mucosa-associated lymphoid tissue (MALT) lymphoma, eight by diffuse large B-cell lymphoma, and three by high-grade lymphoma with low-grade component, all treated with a stomach-conservative approach. One hundred and twenty matched evaluations with both EUS and endoscopy with biopsy (E-Bx) were performed, according to validated guidelines and clinical judgment. At a median follow-up of 87 months ranged between 9.5 and 166 months, the analysis of progression-free survival and disease-free survival showed a strict relationship between the persistence of EUS abnormalities and the clinical outcome in patients with MALT lymphoma (p = 0.0079; p = 0.02) but not in patients with high-grade lymphoma. In conclusion, EUS evaluation does not seem reliable in follow-up management of high-grade lymphomas, although it could have a great clinical impact in the management of MALT lymphoma.