Isolated adrenocorticotropic hormone (ACTH) deficiency (IAD) is extraordinarily rare, and the clinical manifestations of its accompanying adrenal insufficiency are diverse. Early-onset forms of IAD have been linked to mutations in the Tpit transcription factor gene TPIT; however, the genetic basis of juvenile- or late-onset IAD is unknown. Herein, we describe a case of a peripubertal girl with IAD and a normal TPIT gene who presented with an acute neurologic emergency, demonstrating both the variable clinical presentation of IAD and the need for continued investigation into the molecular mechanisms underlying juvenile- and late-onset IAD.