Hypothyroidism over a lifetime is rare. Such a case is reported due to post-coupling dyshormonogenesis in a patient who had developed an aortic aneurysm. It is proposed that the aortic aneurysm could have arisen as a direct consequence of the hypothyroidism. Furthermore, Reilly bodies, which are deposits of mucopolysaccharide, were found in the peripheral blood leucocytes; these have never been previously described in hypothyroidism. It is suggested that they may reflect an underlying disturbance in mucopolysaccharide turnover which could have resulted in weakening of the aortic wall and aneurysmal formation.