Beginning in the early 1950s, a series of epidemiological, biochemical, pathological, and animal studies demonstrated a link between cigarette smoking and lung cancer. A number of reputable scientists challenged these findings, but for a variety of reasons, including the behavior of the tobacco industry, historians have assumed that these objections were insubstantial and disingenuous. Viewing these objections in scientific and medical perspective, however, suggests that there was a legitimate and reasonable scientific controversy over cigarette smoking and lung cancer in the 1950s and early 1960s. That controversy had important consequences. A new chronic disease epidemiology emerged, transforming the role and importance of epidemiology to medical research. This new epidemiology supplemented Koch's postulates, establishing a statistical method that allowed for linking environmental factors to the etiology of chronic diseases. The 1964 report to the surgeon general, Smoking and Health, represented the denouement and codification of these developments. This reexamination of the scientific controversy over smoking in the 1950s and early 1960s provides an important context for understanding the subsequent public relations battles between the tobacco industry and public health after 1964.