Thyrotoxicosis due to Graves disease is a relatively common endocrine disorder. The occurrence of a prolactinoma with co-secretion of growth hormone (GH) is on the other hand, rare. We report the rare co-existence of Graves' disease in a patient with macroprolactinoma and GH hypersecretion and describe the successful response to medical therapy with dopamine agonist and antithyroid therapy. We hypothesize that hyperprolactinaemia played a role in promoting autoimmune thyroid disease in our patient and that treatment of hyperprolactinaemia may have been important in suppressing autoimmune disease activity in Graves' disease. This case also reflects on the close and complex interactions between thyroid hormones, prolactin (PRL), GH and testosterone (T).