Paris in the 1920s proved the most influential decade of Fitzgerald's development. Fitzgerald made several excursions to Europe, mostly Paris and the French Riviera, and became friends with many members of the American expatriate community in Paris, notably Ernest Hemingway. Fitzgerald's friendship with Hemingway was quite vigorous, as many of Fitzgerald's relationships would prove to be. Hemingway did not get on well with Zelda. In addition to describing her as "insane" he claimed that she "encouraged her husband to drink so as to distract Fitzgerald from his work on his novel", the other work being the short stories he sold to magazines. Like most professional authors at the time, Fitzgerald supplemented his income by writing short stories for such magazines as The Saturday Evening Post, Collier's Weekly, and Esquire, and sold his stories and novels to Hollywood studios. This "whoring", as Fitzgerald and, subsequently, Hemingway called these sales, was a sore point in the authors' friendship. Fitzgerald claimed that he would first write his stories in an authentic manner but then put in "twists that made them into salable magazine stories".
Although Fitzgerald's passion lay in writing novels, only his first novel sold well enough to support the opulent lifestyle that he and Zelda adopted as New York celebrities. (The Great Gatsby, now considered to be his masterpiece, did not become popular until after Fitzgerald's death.) Because of this lifestyle, as well as the bills from Zelda's medical care when they came, Fitzgerald was constantly in financial trouble and often required loans from his literary agent, Harold Ober, and his editor at Scribner's, Maxwell Perkins. When Ober decided not to continue advancing money to Fitzgerald, the author severed ties with his longtime friend and agent. (Fitzgerald offered a good-hearted and apologetic tribute to this support in the late short story "Financing Finnegan".)
Fitzgerald began working on his fourth novel during the late 1920s but was sidetracked by financial difficulties that necessitated his writing commercial short stories, and by the schizophrenia that struck Zelda in 1930. Her emotional health remained fragile for the rest of her life. In February 1932, she was hospitalized at the Phipps Clinic at Johns Hopkins in Baltimore, Maryland. During this time, Fitzgerald rented the "La Paix" estate in the suburb of Towson, Maryland to work on his latest book, the story of the rise and fall of Dick Diver, a promising young psychiatrist who falls in love with and marries Nicole Warren, one of his patients. The book went through many versions, the first of which was to be a story of matricide. Some critics have seen the book as a thinly-veiled autobiographical novel recounting Fitzgerald's problems with his wife, the corrosive effects of wealth and a decadent lifestyle, his own egoism and self-confidence, and his continuing alcoholism. Indeed, Fitzgerald was extremely protective of his "material" (i.e., their life together). When Zelda wrote and sent to Scribner's her own fictional version of their lives in Europe, Save Me the Waltz, Fitzgerald was angry and was able to make some changes prior to the novel's publication, and convince her doctors to keep her from writing any more about what he called his "material", which included their relationship. His book was finally published in 1934 as Tender Is the Night. Critics who had waited nine years for the followup to The Great Gatsby had mixed opinions about the novel. Most were thrown off by its three-part structure and many felt that Fitzgerald had not lived up to their expectations. The novel did not sell well upon publication but, like the earlier Gatsby, the book's reputation has since risen significantly. Fitzgerald's alcoholism and financial difficulties, in addition to Zelda's mental illness, made for difficult years in Baltimore. He was hospitalized nine times at Johns Hopkins Hospital, and his friend H.L. Mencken noted in a 1934 letter that "The case of F. Scott Fitzgerald has become distressing. He is boozing in a wild manner and has become a nuisance."