His book, The Modern Treatment of Nervous and Mental Diseases, which he co-authored with lifelong collaborator William Alanson White, has been a classic in the field, with many reprintings.
A quite heterodox journal (as it still is), the Psychoanalytic Review continued to publish translations of work by dissidents such as C. G. Jung and Alfred Adler long after they had seceded from orthodox Freudianism.
Not an important theoretician in any of the fields in which he practiced, Jelliffe was significant more as a behind-the-scenes mover, especially through his translations and the serials that he owned and edited.
He amassed an enormous library of books, journals, and offprints (well over ten tons in weight), which must surely have been the largest and most important collection in private hands in North America in the early 20th century.
Jelliffe's savings were wiped out by the stock market crash in 1929, so he was forced to continue working into his late seventies.