The development of malignancy, particularly lymphoma, is the most serious complication to affect patients with coeliac disease. Although the association has been known for about 40 years, there are still gaps in our understanding. The prevalence of lymphoma and why only some coeliac patients develop this are not clear but environmental and genetic factors must be at work. Based on data from a large coeliac clinic in Derby, about 55 lymphomas per year would arise in the coeliac population of the United Kingdom, of which half would affect the small bowel. Whether patients with coeliac disease who have atypical or no symptoms at diagnosis, are at the same risk as those who are diagnosed as a result of classical symptoms as was more the case in the past, is not known. Some patients, however do have coeliac disease and lymphoma diagnosed at the same presentation. This consideration has implications for initiating screening programmes to detect coeliac disease and thus offer patients a gluten-free diet early that would help to reduce the risk of lymphoma from developing. In this context, case-finding rather than blanket population screening is to be recommended on present evidence. Research into the role of intraepithelial lymphocytes in the genesis of lymphoma has indicated that non-responsive coeliac disease (refractory sprue) and ulcerative jejunoileitis (ulcerative jejunitis) are part of the lymphoma spectrum. The diagnosis of lymphoma can be difficult and the prognosis, in general, is poor, although with modern chemotherapeutic regimes and surgery in selected cases, long-term survival is possible. The best option is to try and prevent lymphoma from arising by advising all patients to adhere to a strict gluten-free diet. Malignant complications of coeliac disease are uncommon but will continue to challenge clinicians and clinical scientists. Unravelling the mechanisms that contribute to the development of lymphoma and other tumours in coeliac disease may well contribute to a wider understanding of oncogenesis.