We analysed a cross-sectional telephone survey of U.S. adults to assess the impact of selected characteristics on healthcare-seeking behaviours and treatment practices of people with influenza-like illness (ILI) from September 2009 to March 2010. Of 216 431 respondents, 8·1% reported ILI. After adjusting for selected characteristics, respondents aged 18–64 years with the following factors were more likely to report ILI: a diagnosis of asthma [adjusted odds ratio (aOR) 1·88, 95% CI 1·67–2·13] or heart disease (aOR 1·41, 95% CI 1·17–1·70), being disabled (aOR 1·75, 95% CI 1·57–1·96), and reporting financial barriers to healthcare access (aOR 1·63, 95% CI 1·45–1·82). Similar associations were seen in respondents aged ⩾65 years. Forty percent of respondents with ILI sought healthcare, and 14% who sought healthcare reported receiving influenza antiviral treatment. Treatment was not more frequent in patients with high-risk conditions, except those aged 18–64 years with heart disease (aOR 1·90, 95% CI 1·03–3·51). Of patients at high risk for influenza complications, self-reported ILI was greater but receipt of antiviral treatment was not, despite guidelines recommending their use in this population.