An observational study was conducted in response to public concern regarding the release of both known and suspected environmental carcinogens following the terrorist attacks of September 11, 2001, at the World Trade Center (WTC) in New York, NY, and the potential increase of cancer incidence among exposed individuals. The study subjects were New York state residents enrolled in the WTC Health Registry from 2003-2004 (N = 55,778). The cohort was divided as rescue and recovery workers (n = 21,850) and those not involved in rescue and recovery (n = 33,928). All were followed through December 31, 2008. Standardized incidence ratios (SIRs) made adjustments for age, race and ethnicity, and gender; were computed with 2003-2008 New York state rates as reference; and focused on diagnosed cancers in 2007-2008 as most likely related to exposure during September 11, 2001, and the aftermath. The total and site-specific incidence rate differences per 100,000 person-years between the study population and the New York state population in 2007-2008 also were calculated.