This study explores some of the important questions raised but not answered in William Canniff's standard century-old study, The Medical Profession in Upper Canada, 1783-1850. Primarily based on the original medical licenses issued between 1819 and 1841, an array of manuscript material belonging to the Civil Secretary of Upper Canada and the Colonial Office, and documents pertaining to the Medical Board of Upper Canada, this article argues that the disallowance of legislation for the establishment of a colonial College of Physicians and Surgeons in 1839 can only be fully understood in the context of demographic, political, and medical developments which included factors such as ethnicity, tensions between the colony and mother country, and rivalry between medical schools. It explains why the issues of the 1830s continued into the 1840s and undermined any possibility by the profession of forming a single, self-regulating, and unified medical body for licensing and educating practitioners.