INTRODUCTION: We describe smoking prevalence and secondhand smoke (SHS) exposure among adult nonsmokers in New York City (NYC) across key demographic strata and compare exposure estimates with those found nationally. METHODS: We used serum cotinine data from the 2004 NYC Health and Nutrition Examination Survey (n = 1,767 adults aged 20 years or older) and the 2003-2004 National Health and Nutrition Examination Survey (n = 4,476 adults aged 20 years or older) to assess and compare smoking prevalence and the prevalence of elevated cotinine levels (> or =0.05 ng/ml) among nonsmokers. We conducted multivariate logistic regression to assess independent predictors of elevated cotinine levels in NYC. RESULTS: Although the smoking prevalence in NYC was lower than that found nationally (23.3% vs. 29.7%, p < .05), the proportion of nonsmoking adults in NYC with elevated cotinine levels was greater than the national average overall (56.7% vs. 44.9%, p < .05) and was higher for most demographic subgroups. In NYC, the highest cotinine levels among nonsmokers were among adults aged 20-39 years, males, and Asians. DISCUSSION: Although NYC enacted comprehensive smoke-free workplace legislation in 2003, findings suggest that exposure to SHS remains a significant public health issue, especially among certain subgroups. The finding of a higher prevalence of SHS exposure in NYC despite lower smoking rates is puzzling but suggests that SHS exposure in dense, urban settings may pose a particular challenge.