We report a case of a 25-year-old man who presented with a large rectal bleed and positive Meckel's scan followed by surgical excision of a Meckel's diverticulum. The diverticulum was lined by gastric body type mucosa showing evidence of active chronic gastritis associated with the presence of Helicobacter pylori organisms, these being identified immunohistochemically with a specific polyclonal antibody. We have reviewed another 21 cases of Meckel's diverticula removed at St Vincent's Hospital between 1984 and 1997: in nine of these cases the diverticulum was lined by ectopic gastric body type mucosa and in one of these there was an active chronic gastritis associated with Helicobacter pylori. There has been considerable controversy regarding both the presence and significance of Helicobacter organisms in Meckel's diverticula. This is the first study to use immunohistochemistry specifically to identify Helicobacter pylori within two cases of Meckel's diverticula. Both cases demonstrated an active chronic gastritis present within the gastric body type mucosa, thus suggesting that the organisms play a pathogenic role.