Context: Body fat and body composition distribution patterns affect diabetes risk and glycemic control, but most studies use proxy measures (e.g., body mass index). Objective: This study examined the association of percent body fat and lean mass with glycated hemoglobin (HbA1c) in US adults. Design: The National Health and Nutrition Examination Survey (NHANES) is a program of crosssectional studies that enroll nationally representative samples of the US civilian noninstitutionalized population. Setting: NHANESis designed to assess the health status of adults and children throughout the United States. Participants: This study included 11,125 participants aged 18 to 69 years from the 1999 through 2006 NHANES, comprising 846 persons with diagnosed diabetes and 10,125 without diabetes. Main Outcome Measures: Total and abdominal (trunk) percent body fat and lean mass were measured using dual-energy x-ray absorptiometry. Linear and logistic regression analyses were used to examine their association with HbA1c. Results: Among those without diagnosed diabetes, total and trunk percent body fat, as well as trunk and total lean mass, were strongly associated with elevated HbA1c; odds ratios per 5% increment for the association of percent body fat with HbA1c > 5.7% (39 mmol/mol) ranged from 1.60 to 2.01 across age and sex categories. Among adults with diabetes, higher total percent fat was associated with higherHbA1c in males age < 40 years and higher trunk fat was associated with higher HbA1c in females across age categories. Conclusions: Lifestyle interventions to lower HbA1c should consider targeting both weight loss and body composition.