INTRODUCTION: Low-carbohydrate diets (LCDs) have regained popularity in recent years, but public awareness and perceived healthfulness of LCDs have not been explored. We describe population awareness, use, and perceptions of the healthfulness of LCDs and examine differences by sociodemographic and communication variables. METHODS: Nationally representative data from the Health Information National Trends Survey (HINTS 2005) were analyzed by using multivariate logistic regression to examine independent correlates of awareness, use, and perceptions of the healthfulness of LCDs. RESULTS: Awareness of LCDs in the United States was high (86.6%). Independent correlates of awareness included being a college graduate, being non-Hispanic white, and having a high body mass index (BMI). Among respondents who were aware of LCDs, approximately 17% had tried LCDs during the last year. Independent correlates of LCD use included being a woman and having a high BMI. One-third of respondents who were aware of LCDs agreed that they are a healthy way to lose weight. Independent correlates of perceived LCD healthfulness included not being a high school graduate and being likely to change behavior in response to new nutrition recommendations. CONCLUSION: This study is among the first to explore correlates of awareness, use, and perceptions of LCDs in a nationally representative sample. Despite high levels of awareness of LCDs, these diets are not used frequently and are not perceived as being healthy.