Objectives: To describe the prevalence and characteristics related to indoor tanning use among adults in the United States in the past year. DESIGN: Cross-sectional study. SETTING: Health Information National Trends Study, 2005. PARTICIPANTS: The study included 2869 participants who were white and aged 18 to 64 years; a random subset of 821 participants were also asked questions about skin cancer prevention knowledge and attitudes. MAIN OUTCOME MEASURES: The study assessed the prevalence of self-reported use of indoor tanning in the past 12 months and its associations with demographic and lifestyle factors, knowledge, and attitudes. RESULTS: Overall, 18.1% of women and 6.3% of men reported tanning indoors in the past 12 months. Women who were older, were less educated, had lower income, and used sunscreen regularly were less likely to report the behavior, while women residing in the Midwest and the South and who used spray tanning products were more likely to report the behavior. Men who were less likely to report the behavior were older and obese but more likely to report the behavior if they lived in metropolitan areas and used spray tanning products. In an open-response format, only 13.3% of women and 4.2% of men suggested that avoidance of tanning bed use could reduce their risks of skin cancer. Greater skin cancer knowledge and higher perceived risk of skin cancer were inversely associated with the behavior in women. CONCLUSIONS: Prevalence and some characteristics associated with indoor tanning use, such as sunscreen use, differed between women and men in the United States. Most adults did not volunteer avoidance of tanning bed use to prevent skin cancer. Clinician-patient communication on risks of indoor tanning may be helpful to reduce indoor tanning use.