We describe nine cases of gastric adenocarcinoma (six intestinal and three diffuse type) occurring in the stomach synchronously with primary low grade B-cell lymphoma of mucosa associated lymphoid tissue. In four cases the two neoplasms were admixed to form collision tumours. Where collision was present between lymphoma and adenocarcinoma of intestinal type no lymphoepithelial lesions were seen involving neoplastic glands. Helicobacter pylori-like organisms were seen in seven cases (78%) which is consistent with an aetiological role for this organism in both tumours in the stomach.