The observation that low birth weight is associated with cardiovascular disease and its risk factors has formed the basis for the 'developmental origins' hypothesis. This hypothesis suggests that the operation of adverse influences during intrauterine life leads to permanent alterations in structure and physiology of the adult phenotype which predispose to a range of common adult diseases. The process is known as developmental plasticity or programming and is strongly supported by studies in experimental animals. Recent evidence suggests that the same processes may affect the development of the immune system and play a part in the pathogenesis of autoimmune disease. Animal studies show that the intrauterine environment has powerful and long-lasting effects on many aspects of immune function. The corresponding human evidence, though preliminary, suggests that birth weight or other markers of the early environment are associated with a range of autoimmune diseases.