Oliver Wendell Holmes, Sr. (1809-1894) was a Boston physician, a professor of medicine at the Harvard Medical School, and a writer of prose and poetry for general audiences. He was also one of the most famous American wits of the nineteenth century and a celebrity not bashful about exposing costly, absurd, and potentially harmful medical fads. One of his targets was phrenology, and the current article examines how he learned about phrenology during the 1830s as a medical student in Boston and Paris, and his head-reading with Lorenzo Fowler in 1858. It then turns to what he told readers of the Atlantic Monthly (in 1859) and Harvard medical students (in 1861) about phrenology being a pseudoscience and how phrenologists were duping clients. By looking at what Holmes was stating about cranioscopy and practitioners of phrenology in both humorous and more serious ways, historians can more fully appreciate the "bumpy" trajectory of one of the most significant medical and scientific fads of the nineteenth century.