Vocal cord paralysis associated with goiter usually indicates the presence of a malignancy. Pediatric patients retain significant thymic tissue that regresses only later in life. This thymic tissue can develop significant hyperplasia during an acute autoimmune process. We describe a case of a 17-year-old girl who presented with a goiter secondary to severe Graves' disease and a 2-month history of hoarseness, choking on liquid intake, and small-volume vomiting especially after eating. She demonstrated a left vocal cord paralysis probably secondary to a unilateral left recurrent laryngeal nerve palsy. A marked enlargement of the thymus was discovered on thoracic imaging. Treatment was initiated with methimazole, with near complete remission of her vocal cord paralysis within 3 months. Given the immunomodulatory effects of methimazole, a potential mechanism of the left recurrent laryngeal nerve palsy was autoimmune hyperstimulation of the thymus and consequent hyperplasia, resulting in distension of the nerve. Attenuation of the hyperactive immune process with methimazole may have resulted in regression of the mass effect of the thymus and associated reduction of the nerve distension. This case illustrates the unique risk of left recurrent laryngeal nerve palsy in pediatric patients with an acute immune stimulation and hyperplasia of the thymus and the reversibility in the context of mitigation of the immune hyperactivity. Methimazole may be an optimal initial treatment choice in pediatric patients with Graves' disease and left recurrent laryngeal nerve palsy. Pediatrics 2013;132:e1704-e1708 Dr Chiu provided the endocrinology consultation for the patient, conceptualized the significance of the case report, and drafted the initial manuscript; Dr Ledbetter provided the general surgery consultation for the patient and reviewed and revised the manuscript; Dr Richter provided the initial medical evaluation for the patient and reviewed and revised the manuscript; Dr Iyer contributed a radiology assessment of the patient' s imaging and reviewed and revised the manuscript; Dr Merati provided the otolaryngology consultation for the patient and reviewed and revised the manuscript; and all authors approved the final manuscript as submitted.www.pediatrics.org/cgi