Epidemiology has been described as “the diagnostic discipline of mass disease.” It comes therefore as a surprise that most modern epidemics have not been diagnosed by epidemiologists but rather by other experts—and only after a long delay. Epidemiologists have also missed the recent declines in the incidence of major chronic diseases, in particular coronary heart disease, dementia, and Alzheimer’s. In this talk, Albert Hofman evaluates this evidence as well as that provided by the by the current opioid epidemic in the United States, the epidemic of obesity and related type 2 diabetes, and asks the question: “Why are epidemiologists so bad at epidemics?”