Simpson-Golabi-Behmelsyndrome is a rare, X-linked recessive syndrome associated with mutations in the genes encoding glypican 3 (GPC3). The majority of cases have been described in pediatric males, with those affected showing manifestations of overgrowth, congenital heart defects, and increased incidence of neoplasia. Due to the X-linked nature of this disorder, penetrance is not well understood in female cases. Very few cases of female presentations of Simpson-Golabi-Behmelsyndrome have been described. We present a case of GPC3 gene mutation suggestive of Simpson-Golabi-Behmelsyndrome in an adult female patient, diagnosed based on genetic testing performed due to a diagnosis of sebaceous carcinoma.