Long after the leading causes of death in the United States shifted from infectious diseases to chronic diseases, many public health agencies have not established effective policies and programmes to prevent current health problems. Starting in 2002, the New York City health department, an agency with a long history of innovation, undertook initiatives to address chronic disease prevention and control, as well as to modernize methods to address persistent health problems. All the initiatives relied on an expansive use of epidemiology; actions to prevent disease were based on policy change to create health-promoting environments as well as engagement with the health care system to improve its focus on prevention. Examples of policy-based initiatives are: a multi-component tobacco control programme that included a tax increase, a comprehensive smoke-free air law, hard-hitting anti-tobacco advertising and cessation services; elimination of trans fats from restaurants and a mandate that restaurants post-calorie information on menu boards. Examples of health care initiatives are public health 'detailing' to primary care providers, creation of a city-wide diabetes registry and development of a public health-oriented electronic health record. The infrastructure needed by local health departments to prevent chronic diseases and other modern health problems includes strong information technology systems, skillful epidemiology, expertise in communications using modern media, policy-making authority and, most importantly, political support.