BACKGROUND: Low grade gastric MALT lymphoma is associated to infection with Helicobacter pylori. Also, H. pylori eradication can produce histologic regression of the lymphoma. PATIENTS AND METHODS: This study reports the follow-up of a prospective series of 11 patients with low grade gastric MALT lymphoma, stage I, treated with eradicative therapy for H. pylori. After treatment, patients were followed up with sequential endoscopies to asses the histological and molecular regression of the lymphoma, using a score of the histological lesions and the amplification of the IgH gene with PCR analysis. RESULTS: Helicobacter pylori was eradicated in all patients. In 10(90.9%) histological regression of the lymphoma was demonstrated, in 6 of them in the first control after treatment. In the 10 patients with histological response, PCR analysis demonstrated a polyclonal rearrangement of the IgH gene in 6 (60%) and a clonal band in 4 (40%), that eventually disappeared at 12 (SD 4) months after treatment. In 4 patients with a previous polyclonal rearrangement, a clonal band was occasionally detected in any sequential controls; in 2 of these cases the clonal band disappeared 5 and 7 months after treatment and in the remaining 2 its evolution is not yet known. Nine patients have been followed up and are in remission 18 (SD 8) months after treatment. CONCLUSIONS: Eradication of H. pylori can produce histologic regression in stage I low grade gastric MALT lymphoma, and should be the first therapeutic option. Despite histological regression of the lymphoma, PCR analysis can detect a clonal rearrangement of the IgH gene in 40% of the cases, but its significance remains unknown. Sequential and prolonged follow-up is essential to assess whether this lymphoma can be actually cured with eradication therapy for H. pylori.