Objective To measure knowledge of the health consequences of obesity among overweight/obese Black and Hispanic adults and examine the relationship to prior weight loss. Methods Knowledge of the health consequences of obesity was assessed among 410 Black and Hispanic adults with BMI ≥ 25 kg/m2 enrolled in a behavior change weight loss study. The relationship between obesity risk knowledge and previous weight loss was also examined. Results The majority of participants were knowledgeable of the risk of hypertension (94%), diabetes (96%), high cholesterol (91%), joint pains/arthritis (89%) and sleep apnea (89%) associated with obesity. Among post-menopausal age women, 53% were aware of the increased risk of breast cancer. There was no significant relationship between obesity risk knowledge and previous weight loss of 10 pounds or more (OR= 1.075, 95% CI: [0.808, 1.430]). Conclusions We found that knowledge of the health consequences of obesity was high, except for knowledge of the risk of breast cancer. Obesity risk knowledge was not associated with past weight loss. Practice implications Further health education is needed regarding the increased risk of breast cancer associated with obesity. Our data suggest that knowledge of the health consequences of obesity is not associated with weight loss success.