Patients with primary hypothyroidism may also have other underlying associated endocrinopathies, which are important to exclude. A 15-y-old girl presented w ith clinical and biochemical evidence of hypothyroidism. Conclusion: Thyroxine r eplacement unmasked Addison’s disease and precipitated an acute adrenal crisis. On physiological steroid replacement therapy, her “hypothyroidism”resolved. Patients with primary hypothyroidism may also have other underlying associated endocrinopathies, which are important to exclude. A 15-y-old girl presented w ith clinical and biochemical evidence of hypothyroidism. Conclusion: Thyroxine r eplacement unmasked Addison’s disease and precipitated an acute adrenal crisis. On physiological steroid replacement therapy, her “hypothyroidism” resolved.