Purpose The purpose of this cross-sectional study was to investigate whether obesity is associated with suicide attempt in a nationally representative sample of U.S. adults. Methods From the 2004–2005 National Epidemiologic Survey of Alcohol and Related Conditions Wave 2 data (n = 34,653 adults), survey responses were extracted on suicide attempt (ever, recent [≤ 2 years]), demographic (age, sex, race/ethnicity), mental disorders (internalizing, personality, substance abuse), and psychosocial factors (e.g., abuse, trauma, sexual identity). Current body mass index (BMI) categorized participants as obese (≥ 30 kg/m2) or non-obese (2). Odds ratio [95% confidence interval] of suicide attempt by obesity status was calculated by logistic regression, while adjusting for mental health, demographic, and psychosocial confounders. Results Ever and recent suicide attempt prevalence was 3.4% and 3.1%, respectively, and the obesity prevalence 28%. Compared to non-obese adults, obese adults were 1.43 [1.20–1.69] times and 1.40 [0.90–2.18] times more likely to have ever, and recently, attempted suicide, respectively. Among the obese, middle-age (36–55 years) adults were 0.64 [0.31–0.92] times less likely to have ever-attempted suicide than older (> 55 years) adults. Only 15% of the obesity’s association with lifetime suicide attempt was mediated by mental illnesses. Conclusion Current-obesity is associated with lifetime suicide attempt among U.S. adults, even after adjustment for mental health, demographic, and psychosocial confounders. Further research on the temporality and causality of this association is needed.