Sturge-Weber syndrome has been found to result in hypothalamic-pituitary dysfunction including central hypothyroidism. Because central hypothyroidism is more prevalent in Sturge-Weber syndrome than in the general population, we routinely evaluated thyroid function. Here we describe 5 children with Sturge-Weber syndrome on anticonvulsants and diagnosed with hypothyroidism based on thyroid function testing. All 5 patients were eventually tested utilizing the more accurate free thyroxine equilibrium dialysis assay. Results indicated that only 2 of the 5 patients, who exhibited the most severe symptoms, had true hypothyroidism. This case series demonstrates the benefits of using the free thyroxine by equilibrium dialysis when testing Sturge-Weber syndrome patients on antiepileptic medications. This testing algorithm is more cost-effective and also improves the quality of care by providing an accurate diagnosis more quickly. In addition, we propose consideration of this testing method in any patient taking anticonvulsants, most notably oxcarbazepine.