Frank R. Kleffner (October 10, 1925 – June 12, 2015) was an American pathologist who was a professor at Washington University in St. Louis, noted for his contributions in the fields of speech and language pathology and hearing. His work with William Landau and Harold Klawans advanced his career beyond regular work in a neurology clinic. His name became well known for a controversial treatment for a disease affecting children under the age of five and causing acquired aphasia (Landau–Kleffner syndrome).