William Osler is accepted as a quintessential physician across the history of medicine. As the father of modern Hippocratic medicine, he moved 19th century foundations of medical education from classrooms to patients’ bedsides (fi gure), introduced routine uses of the laboratory and autopsy as part of a physician’s ongoing education and practice, and brought scholarship, humility, and humanities into the doctor–patient relationship. He was beloved by those who knew him and respected by his and following generations. He provided care for the patient by fi rst caring for the person. Osler still receives justly deserved accolades for advancing the places of science, humanities, and professionalism in medicine (see appendix for references). Osler is less frequently acknowledged for his error controls, variational biology, scientifi c methods, and humanism—issues problematic for modern medicine. To preserve its Hippocratic roots, modern medicine must be professional in its scientifi c and humanistic care of patients and support research and patient care with sound business practices. Beginning in the late 20th century one after another destabilising problems complicated the practice of medicine. Inadequate numbers of general practitioners and the threat of losing its professionalism became real for American medicine. Today, medicine is subject internationally to various challenges: dysfunctional government regulations, uncontrolled costs, serious morbidity and mortality from medical errors, a dearth of primary care physicians, and, perhaps most portending of continued diffi culties in the USA, the failure of health care to become organised as an economically stable and functional system of care. Medicine has to pursue professionalism, tolerate and be able to accommodate those who would make it or treat it as a business, do so without becoming a business, and justify empirically quality in its health care and business practices. Legislation, regulations, and special interests that undermine professionalism are not in the public’s best interests. To preserve its professionalism, medicine needs public understanding of how its professionalism and public support generate improved health and care, and reduced costs. A two-way street leads to medicine’s future. As the centennial of his death comes closer, Osler provides us with sound foundations for preserving medical professionalism. Osler teaches us to make eff ective uses of science and humanism in patient care and research, to deserve public support, and to manage health care and government relations without losing our professionalism. William Osler (1849–1919) was born in rural Ontario, Canada, the son of an Anglican clergyman. Shaped by boyhood access to a microscope, studies of polyzoa, and later exposures to Sir Thomas Browne, Osler chose medicine. In later life he characterised his career as the childhood reduction of sap to maple syrup adapted to open new scientifi c vistas in medicine. After publishing as a young naturalist, Osler enrolled at Toronto Medical School. Fascinated with anatomy, parasites, the humanities, but unimpressed with lectures from faculty, he transferred to McGill for bedside experiences brought there from Edinburgh, UK. After graduation he studied in Europe for 2 years before joining the medical faculty at McGill. Osler, acknowledged for his learning, by 1883 had become a professor at McGill and one of only two Canadian fellows of the British Royal College of Physicians. In this decade after graduation Osler put a stamp on McGill medical education that lasted throughout the 20th century. Similarly, as a professor at Philadelphia and later Hopkins, he revolutionised American medical education by teaching students at the bedside. In 1884, on the fl ip of a coin, Osler left Montreal for the larger centre at the University of Pennsylvania. Then, in 1888, Osler eagerly accepted an opportunity to become professor at the planned Johns Hopkins Hospital and Medical School. In 1905, encouraged by his wife to escape an ever-demanding Baltimore practice, he accepted the Regius Professorship of Medicine at Oxford University. He remained at Oxford until his death in 1919. Osler, never one to evidence his eminence to others, lived simply, saw rich and poor in his practice, and did not attend his baronet ceremony in 1911. In learning, teaching, and practice Osler linked the clinic, laboratory, autopsy room, and library. Osler’s values—learning at the patient’s bedside, observation, cautious induction, confi rmation of impressions from patients, library, and laboratory, expansion of knowledge by correlation of autopsy fi ndings with clinical observations, and working with a love of every person equally without regard to rank—still defi ne for many how medicine is best practised. Osler admired Sydenham, the English Hippocrates, as “a man of many doubts.” Persuaded by what he could and could not learn from patients, books, and laboratories, Osler tempered his enthusiasm for science with controlled skepticism. These conditioned views framed how he practised medicine. He communicated his practices in practical and timeless precepts. Decades later at McGill, those who knew him, such as W W Francis, and teachers who emulated him used Lancet 2014; 384: 2260–63