Thyroid abnormalities and Takayasu arteritis (TA) have been reported separately in patients with Crohn disease (CD). We report two patients with hyperthyroidism, CD and Takayasu arteritis and discuss hypothetical mechanisms. Case 1. A thyrotoxic goiter was diagnosed in 1987 in a 34-year-old woman treated since 1969 for severe CD and TA. Iodine urinary excretion was 405 microg/mL (20-500). Anti-thyrotropin receptor (TRAK) and anti-thyroid antibodies were not detectable. The ultrasonography showed a nodule in the right lobe of the thyroid and two nodules in the left lobe. A 123I thyroid scan showed a multinodular goiter with no hot nodule. She was treated successfully with propylthiouracile until 1991, when a new episode of thyrotoxicosis led to a subtotal thyroidectomy. Case 2. Hyperthyroidism was diagnosed in February 2000 in a 49-year-old woman treated for CD and TA, both diagnosed in 1980. TRAK and anti-thyroid peroxydase antibodies were not detectable. The ultrasonography disclosed a normal thyroid volume with an inhomogeneous parenchymal structure and nodular images in both lobes. A 123I thyroid scan showed one hot nodule in the lower part of each lobe. A subtotal thyroidectomy was performed. The association of these three diseases may not be fortuitous, possibly explained by genetic predisposing factors and disease-related iodine deficiency both involving Nuclear Factor kappaB pathway.