Autoimmune thyroid disease (AITD) is common and occurs frequently in conjunction with other diseases. Many putative disease associations have been suggested for AITD but the validity of these associations is not clear in all cases. It is important to define disease associations correctly because this may offer a means to rationally screen for true associations, may shed light on shared pathophysiologic mechanisms and may be important if the associated disease impacts on patient management. This review has examined the evidence base for a large number of the suggested associations.