Hints that the growth of some lymphomas is stimulated by bacterial antigens and can be controlled by treatment with antibiotics first emerged in the 1970s. Subsequently, a specific type of B-cell lymphoma — mucosa-associated lymphoid tissue (MALT) lymphoma — was identified that is associated with bacterial infection and auto-antigen stimulation. This article chronicles the clinical, immunological and molecular developments in our knowledge of MALT lymphoma and the factors that contribute to its pathogenesis.