In this chapter we have outlined the seronegative spondarthritides associated with bowel disease, excluding those discussed in separate chapters. Although, traditionally, Crohn's disease and ulcerative colitis have been dealt with separately in any discussion of seronegative arthritides, they have been discussed together here for the following reasons. Despite being pathologically distinct they show remarkable similarity in extraintestinal manifestations including any associated arthritis. Any observed differences in prevalence rates of arthritis may be secondary to the relative difficulty in diagnosing Crohn's disease, and most of the important prevalence studies were done before the more sophisticated techniques to investigate the bowel became available. This may in part explain the dramatic increase in the world-wide incidence of Crohn's disease seen in the last 30 years, particularly through the 1970s, but which has fallen off recently (Miller et al, 1974). It would seem that the body has a limited means of expressing disease processes. The final common pathway of a number of quite distinct disease entities is the concept of the seronegative spondarthritides. Exactly how the microbiological, immunogenetic and molecular factors interact to produce a particular disease end-point is currently not clearly defined, but with the increasingly sophisticated means to investigate the body at a cellular level the explanations may soon be at hand. Further controlled family studies are also needed to define the genetic relationships more precisely. We may then be able to piece the jigsaw puzzle together.