Coeliac disease is the life-long intolerance to dietary gluten, usually characterized by severe damage to the small-intestinal mucosa. The widespread use of sensitive diagnostic tools, such as the serum anti-gliadin and the anti-endomysial antibodies, has shown not only that coeliac disease is one of the commonest disorders in Western countries but also that this condition is characterized by a higher degree of clinical variability than previously thought (typical, atypical and silent forms). The existence of a latent-potential coeliac disease and even a gluten-sensitive disease with immunological activation of an otherwise normal small-intestinal mucosa has recently been postulated. An increased prevalence of coeliac disease in a number of other disorders has also been reported in both children and adults. The reasons for such a wide clinical heterogeneity are still poorly understood but are likely to depend on both genetic and environmental factors. Further investigations are required to evaluate the impact of undiagnosed, clinically milder forms of coeliac disease on the well-being of the population.