Thymoma is a diagnosis most often made in adults, and is exceedingly rare in children. The diagnosis of a thymoma is often times linked to an autoimmune process, and the association of thymoma and myasthenia gravis in children has been previously reported. We present the first description of a child of a parent with Isaacs syndrome (congenital or acquired neuromyotonia) presenting with a thymoma. In our patient, an evaluation of underlying disease led to a presumptive diagnosis of congenital Isaacs syndrome. This case demonstrates that for the rare child diagnosed with thymoma, evaluation for an underlying neurologic disorder should be considered.